diff --git a/.github/workflows/publish.yml b/.github/workflows/publish.yml
index a7fce5a79..962ebc7c0 100644
--- a/.github/workflows/publish.yml
+++ b/.github/workflows/publish.yml
@@ -30,7 +30,7 @@ on:
 jobs:
   publish:
     name: Publish to Maven repositories
-    uses: SpineEventEngine/config/.github/workflows/publishing.yml@5ddff23286f7f6353d4714b0399ab89109c56c79
+    uses: SpineEventEngine/config/.github/workflows/publishing.yml@3cc29d4e51eb6de7da4234d2677973cead2cea84
     permissions:
       contents: read
       packages: write
diff --git a/buildSrc/src/main/kotlin/io/spine/dependency/local/Compiler.kt b/buildSrc/src/main/kotlin/io/spine/dependency/local/Compiler.kt
index b75c0f1ef..385a12179 100644
--- a/buildSrc/src/main/kotlin/io/spine/dependency/local/Compiler.kt
+++ b/buildSrc/src/main/kotlin/io/spine/dependency/local/Compiler.kt
@@ -60,7 +60,7 @@ object Compiler : Dependency() {
      * The version of the Compiler dependencies.
      */
     override val version: String
-    private const val fallbackVersion = "2.0.0-SNAPSHOT.081"
+    private const val fallbackVersion = "2.0.0-SNAPSHOT.083"
 
     /**
      * The distinct version of the Compiler used by other build tools.
@@ -69,7 +69,7 @@ object Compiler : Dependency() {
      * transitive dependencies, this is the version used to build the project itself.
      */
     val dogfoodingVersion: String
-    private const val fallbackDfVersion = "2.0.0-SNAPSHOT.081"
+    private const val fallbackDfVersion = "2.0.0-SNAPSHOT.083"
 
     /**
      * The artifact for the Compiler Gradle plugin.
diff --git a/buildSrc/src/main/kotlin/io/spine/dependency/local/CoreJvm.kt b/buildSrc/src/main/kotlin/io/spine/dependency/local/CoreJvm.kt
index 94f3d9d68..597049f49 100644
--- a/buildSrc/src/main/kotlin/io/spine/dependency/local/CoreJvm.kt
+++ b/buildSrc/src/main/kotlin/io/spine/dependency/local/CoreJvm.kt
@@ -30,7 +30,7 @@ typealias CoreJava = CoreJvm
 )
 object CoreJvm {
     const val group = Spine.group
-    const val version = "2.0.0-SNAPSHOT.577"
+    const val version = "2.0.0-SNAPSHOT.611"
 
     const val coreArtifact = "spine-core"
     const val clientArtifact = "spine-client"
diff --git a/buildSrc/src/main/kotlin/io/spine/dependency/local/CoreJvmCompiler.kt b/buildSrc/src/main/kotlin/io/spine/dependency/local/CoreJvmCompiler.kt
index 8fc131eaa..ef58eb0a6 100644
--- a/buildSrc/src/main/kotlin/io/spine/dependency/local/CoreJvmCompiler.kt
+++ b/buildSrc/src/main/kotlin/io/spine/dependency/local/CoreJvmCompiler.kt
@@ -34,12 +34,12 @@ object CoreJvmCompiler {
     /**
      * The version used in the build classpath.
      */
-    const val dogfoodingVersion = "2.0.0-SNAPSHOT.099"
+    const val dogfoodingVersion = "2.0.0-SNAPSHOT.104"
 
     /**
      * The version to be used for integration tests.
      */
-    const val version = "2.0.0-SNAPSHOT.099"
+    const val version = "2.0.0-SNAPSHOT.104"
 
     /**
      * The ID of the Gradle plugin.
diff --git a/buildSrc/src/main/kotlin/io/spine/dependency/local/ProtoTap.kt b/buildSrc/src/main/kotlin/io/spine/dependency/local/ProtoTap.kt
index b9e6f18ec..a7b277c26 100644
--- a/buildSrc/src/main/kotlin/io/spine/dependency/local/ProtoTap.kt
+++ b/buildSrc/src/main/kotlin/io/spine/dependency/local/ProtoTap.kt
@@ -26,7 +26,7 @@ package io.spine.dependency.local
 )
 object ProtoTap {
     const val group = Spine.toolsGroup
-    const val version = "0.17.4"
+    const val version = "0.17.5"
     const val gradlePluginId = "io.spine.prototap"
     const val api = "$group:prototap-api:$version"
     const val gradlePlugin = "$group:prototap-gradle-plugin:$version"
diff --git a/buildSrc/src/main/kotlin/io/spine/dependency/local/ToolBase.kt b/buildSrc/src/main/kotlin/io/spine/dependency/local/ToolBase.kt
index 7bd22c472..52b0f2a58 100644
--- a/buildSrc/src/main/kotlin/io/spine/dependency/local/ToolBase.kt
+++ b/buildSrc/src/main/kotlin/io/spine/dependency/local/ToolBase.kt
@@ -32,8 +32,8 @@ package io.spine.dependency.local
 )
 object ToolBase {
     const val group = Spine.toolsGroup
-    const val version = "2.0.0-SNAPSHOT.428"
-    const val dogfoodingVersion = "2.0.0-SNAPSHOT.428"
+    const val version = "2.0.0-SNAPSHOT.451"
+    const val dogfoodingVersion = "2.0.0-SNAPSHOT.451"
 
     const val archive = "$group:archive:$version"
     const val code = "$group:code:$version"
diff --git a/buildSrc/src/main/kotlin/io/spine/dependency/local/Validation.kt b/buildSrc/src/main/kotlin/io/spine/dependency/local/Validation.kt
index 1be9aff47..1b4d5cf49 100644
--- a/buildSrc/src/main/kotlin/io/spine/dependency/local/Validation.kt
+++ b/buildSrc/src/main/kotlin/io/spine/dependency/local/Validation.kt
@@ -27,7 +27,7 @@ object Validation {
     /**
      * The version of the Validation library artifacts.
      */
-    const val version = "2.0.0-SNAPSHOT.469"
+    const val version = "2.0.0-SNAPSHOT.470"
 
     const val group = Spine.toolsGroup
     private const val prefix = "validation"
diff --git a/buildSrc/src/main/kotlin/io/spine/gradle/testing/TestKitCoverage.kt b/buildSrc/src/main/kotlin/io/spine/gradle/testing/TestKitCoverage.kt
index 52f663236..96c0753e3 100644
--- a/buildSrc/src/main/kotlin/io/spine/gradle/testing/TestKitCoverage.kt
+++ b/buildSrc/src/main/kotlin/io/spine/gradle/testing/TestKitCoverage.kt
@@ -35,8 +35,8 @@ import org.gradle.kotlin.dsl.withType
  *     dedicated [AGENT_CONFIGURATION] configuration.
  *  2. Passes the agent JAR path and a per-module exec directory
  *     (`build/`[TESTKIT_COVERAGE_DIR]) to the test JVM as system properties.
- *     The `plugin-testlib` harness reads these and writes a `gradle.properties`
- *     into the worker's Gradle user home that adds `-javaagent:…` to the worker JVM.
+ *     The `plugin-testlib` harness reads these and attaches `-javaagent:…` to the
+ *     worker JVM.
  *  3. Wipes the exec directory at most once per build invocation, from the
  *     `doFirst` of the first `Test` task that actually executes, so stale worker
  *     coverage from a previous run does not accumulate. Two failure modes are
@@ -58,6 +58,11 @@ import org.gradle.kotlin.dsl.withType
  *     coverage. An up-to-date (non-cache) run is unaffected: the previous run's
  *     files remain on disk and the guarded `doFirst` never deletes them.
  *
+ * The method does not choose the TestKit directory of the worker builds.
+ * The `module-testing` and `kmp-module` script plugins point the `Test` tasks
+ * of a module at a shared one (see [useSharedTestKitDir]), which a harness
+ * that passes its own directory to `withTestKitDir(...)` does not use.
+ *
  * The produced `.exec` files are merged into the Kover reports by
  * [io.spine.gradle.report.coverage.KoverConfig]. The agent emits binary
  * execution data rather than an XML report because that is its only file output,
diff --git a/buildSrc/src/main/kotlin/io/spine/gradle/testing/TestKitDir.kt b/buildSrc/src/main/kotlin/io/spine/gradle/testing/TestKitDir.kt
new file mode 100644
index 000000000..d9c60ef97
--- /dev/null
+++ b/buildSrc/src/main/kotlin/io/spine/gradle/testing/TestKitDir.kt
@@ -0,0 +1,84 @@
+/*
+ * Copyright 2026 CodeMatters, Lda.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
+ */
+
+package io.spine.gradle.testing
+
+import org.gradle.api.Project
+import org.gradle.api.tasks.testing.Test
+import org.gradle.kotlin.dsl.withType
+
+/**
+ * Configures the `Test` tasks of this project so that the Gradle TestKit builds
+ * they run use the TestKit directory [shared by all modules][SHARED_TESTKIT_DIR].
+ *
+ * A TestKit directory is the Gradle user home of the builds that
+ * [GradleRunner][org.gradle.testkit.runner.GradleRunner] runs. It holds mostly
+ * Gradle's instrumented copies of the JARs on the classpath of the plugin under
+ * test, and the compiled build scripts of the test projects. When the directory
+ * is empty, the TestKit builds recreate them, which is slow on a CI runner.
+ *
+ * Without the [`org.gradle.testkit.dir`][TESTKIT_DIR_PROPERTY] system property,
+ * TestKit keeps the directory at `build/tmp/<task>/work/.gradle-test-kit`, in
+ * the temporary directory of the `Test` task. So each `Test` task of each module
+ * has its own, which is empty in a fresh checkout and after `clean`. This
+ * function passes the shared directory to the test JVM as that property, which
+ * `GradleRunner.create()` reads. A runner given a directory with
+ * `withTestKitDir(...)` still uses that one.
+ *
+ * The property is set from a `doFirst` action rather than at configuration time,
+ * so it is not a task input. Where TestKit builds keep their caches does not
+ * affect the test results, while the absolute path differs between machines.
+ * As an input, it would only break the reuse of the `Test` task results from
+ * the build cache across machines. A `Test` task that already has the property
+ * keeps its value, so a repeated call has no further effect.
+ *
+ * The function applies to all the `Test` tasks of the project, whether they
+ * run TestKit builds or not, and whether the project collects the coverage of
+ * those builds or not (see [enableTestKitCoverage]).
+ */
+fun Project.useSharedTestKitDir() {
+    val testKitDir = gradle.gradleUserHomeDir.resolve(SHARED_TESTKIT_DIR)
+    tasks.withType<Test>().configureEach {
+        doFirst {
+            if (TESTKIT_DIR_PROPERTY !in systemProperties) {
+                systemProperty(TESTKIT_DIR_PROPERTY, testKitDir.absolutePath)
+            }
+        }
+    }
+}
+
+/**
+ * The name of the system property carrying the absolute path to the TestKit
+ * directory, which `GradleRunner.create()` reads.
+ *
+ * A runner given a directory with `withTestKitDir(...)` uses that one instead.
+ *
+ * @see org.gradle.testkit.runner.GradleRunner.withTestKitDir
+ */
+private const val TESTKIT_DIR_PROPERTY: String = "org.gradle.testkit.dir"
+
+/**
+ * The path, relative to the Gradle user home of the build, of the TestKit
+ * directory shared by the TestKit builds of all modules.
+ *
+ * The directory is placed under `caches/`, which `gradle/actions/setup-gradle`
+ * restores on every run but saves only on the default branch. So a pull request
+ * run starts with a warm directory once a run on the default branch has saved it.
+ * Locally, the TestKit builds of all the repositories that use this `buildSrc`
+ * share it.
+ *
+ * Unlike a directory under `build/`, it is not reset by `clean`. Delete it to make
+ * the TestKit builds start from an empty one.
+ */
+private const val SHARED_TESTKIT_DIR: String = "caches/spine-testkit"
diff --git a/buildSrc/src/main/kotlin/kmp-module.gradle.kts b/buildSrc/src/main/kotlin/kmp-module.gradle.kts
index 0e84f04ac..0574f09dc 100644
--- a/buildSrc/src/main/kotlin/kmp-module.gradle.kts
+++ b/buildSrc/src/main/kotlin/kmp-module.gradle.kts
@@ -27,6 +27,7 @@ import io.spine.gradle.kotlin.setFreeCompilerArgs
 import io.spine.gradle.publish.IncrementGuard
 import io.spine.gradle.report.license.LicenseReporter
 import io.spine.gradle.testing.configureLogging
+import io.spine.gradle.testing.useSharedTestKitDir
 
 /**
  * Configures this [Project] as a Kotlin Multiplatform module.
@@ -167,6 +168,12 @@ tasks {
     }
 }
 
+/**
+ * Gives all the `Test` tasks the TestKit directory shared by all modules,
+ * as `module-testing` does (see [useSharedTestKitDir]).
+ */
+project.useSharedTestKitDir()
+
 /**
  * Overrides the default location of Kotlin sources.
  *
diff --git a/buildSrc/src/main/kotlin/module-testing.gradle.kts b/buildSrc/src/main/kotlin/module-testing.gradle.kts
index add017838..ec256e1cf 100644
--- a/buildSrc/src/main/kotlin/module-testing.gradle.kts
+++ b/buildSrc/src/main/kotlin/module-testing.gradle.kts
@@ -20,10 +20,14 @@ import io.spine.dependency.test.Kotest
 import io.spine.dependency.test.Truth
 import io.spine.gradle.testing.configureLogging
 import io.spine.gradle.testing.registerTestTasks
+import io.spine.gradle.testing.useSharedTestKitDir
 
 /**
  * This convention plugin applies test dependencies and configures test-related tasks.
  *
+ * All the `Test` tasks of the module get the TestKit directory shared by all
+ * modules (see [useSharedTestKitDir]).
+ *
  * The version of the [JUnit] platform must be applied via the [BomsPlugin][io.spine.dependency.boms.BomsPlugin]:
  *
  * ```kotlin
@@ -40,6 +44,7 @@ plugins {
 project.run {
     setupTests()
     forceTestDependencies()
+    useSharedTestKitDir()
 }
 
 dependencies {
diff --git a/config b/config
index 5ddff2328..3cc29d4e5 160000
--- a/config
+++ b/config
@@ -1 +1 @@
-Subproject commit 5ddff23286f7f6353d4714b0399ab89109c56c79
+Subproject commit 3cc29d4e51eb6de7da4234d2677973cead2cea84
diff --git a/docs/dependencies/dependencies.md b/docs/dependencies/dependencies.md
index ceba616e9..cd7ba025f 100644
--- a/docs/dependencies/dependencies.md
+++ b/docs/dependencies/dependencies.md
@@ -1,6 +1,6 @@
 
 
-# Dependencies of `io.spine.tools:archive:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:archive:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : com.google.code.findbugs. **Name** : jsr305. **Version** : 3.0.2.
@@ -832,14 +832,14 @@
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:36 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:46 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:code:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:code:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : com.google.code.findbugs. **Name** : jsr305. **Version** : 3.0.2.
@@ -1655,14 +1655,14 @@ This report was generated on **Tue Nov 03 02:04:36 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:36 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:46 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:fixtures:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:fixtures:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : com.google.android. **Name** : annotations. **Version** : 4.1.1.4.
@@ -2593,14 +2593,14 @@ This report was generated on **Tue Nov 03 02:04:36 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:36 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:46 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:fs:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:fs:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : com.google.code.findbugs. **Name** : jsr305. **Version** : 3.0.2.
@@ -3416,14 +3416,14 @@ This report was generated on **Tue Nov 03 02:04:36 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:36 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:46 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:gradle-plugin-api:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:gradle-plugin-api:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : com.fasterxml.jackson.core. **Name** : jackson-annotations. **Version** : 2.22.
@@ -4345,14 +4345,14 @@ This report was generated on **Tue Nov 03 02:04:36 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:36 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:46 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:gradle-plugin-api-test-fixtures:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:gradle-plugin-api-test-fixtures:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : com.fasterxml.jackson.core. **Name** : jackson-annotations. **Version** : 2.22.
@@ -4865,14 +4865,14 @@ This report was generated on **Tue Nov 03 02:04:36 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:36 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:46 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:gradle-root-plugin:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:gradle-root-plugin:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : com.google.code.findbugs. **Name** : jsr305. **Version** : 3.0.2.
@@ -5736,14 +5736,14 @@ This report was generated on **Tue Nov 03 02:04:36 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:36 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:46 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:intellij-platform:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:intellij-platform:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : be.cyberelf.nanoxml. **Name** : nanoxml. **Version** : 2.2.3.
@@ -6840,14 +6840,14 @@ This report was generated on **Tue Nov 03 02:04:36 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:36 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:47 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:intellij-platform-java:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:intellij-platform-java:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : be.cyberelf.nanoxml. **Name** : nanoxml. **Version** : 2.2.3.
@@ -8719,14 +8719,14 @@ This report was generated on **Tue Nov 03 02:04:36 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:37 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:47 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:java-code:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:java-code:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : com.google.code.findbugs. **Name** : jsr305. **Version** : 3.0.2.
@@ -9596,14 +9596,14 @@ This report was generated on **Tue Nov 03 02:04:37 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:36 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:46 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:jvm-tool-plugins:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:jvm-tool-plugins:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : com.google.code.findbugs. **Name** : jsr305. **Version** : 3.0.2.
@@ -10459,14 +10459,14 @@ This report was generated on **Tue Nov 03 02:04:36 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:36 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:46 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:jvm-tools:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:jvm-tools:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : org.jetbrains. **Name** : annotations. **Version** : 26.1.0.
@@ -11233,14 +11233,14 @@ This report was generated on **Tue Nov 03 02:04:36 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:36 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:46 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:kotlin-code:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:kotlin-code:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : com.google.code.findbugs. **Name** : jsr305. **Version** : 3.0.2.
@@ -12056,14 +12056,14 @@ This report was generated on **Tue Nov 03 02:04:36 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:36 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:46 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:plugin-base:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:plugin-base:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : com.google.code.findbugs. **Name** : jsr305. **Version** : 3.0.2.
@@ -12927,14 +12927,14 @@ This report was generated on **Tue Nov 03 02:04:36 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:36 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:46 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:plugin-testlib:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:plugin-testlib:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : com.google.auto.value. **Name** : auto-value-annotations. **Version** : 1.11.1.
@@ -13901,14 +13901,14 @@ This report was generated on **Tue Nov 03 02:04:36 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:36 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:46 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:proto-code:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:proto-code:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : com.google.code.findbugs. **Name** : jsr305. **Version** : 3.0.2.
@@ -14794,14 +14794,14 @@ This report was generated on **Tue Nov 03 02:04:36 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:36 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:46 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:protobuf-setup-plugins:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:protobuf-setup-plugins:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : com.google.code.findbugs. **Name** : jsr305. **Version** : 3.0.2.
@@ -15677,14 +15677,14 @@ This report was generated on **Tue Nov 03 02:04:36 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:37 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:47 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:psi:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:psi:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : be.cyberelf.nanoxml. **Name** : nanoxml. **Version** : 2.2.3.
@@ -16812,14 +16812,14 @@ This report was generated on **Tue Nov 03 02:04:37 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:37 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:47 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
 
 
 
 
-# Dependencies of `io.spine.tools:psi-java:2.0.0-SNAPSHOT.451`
+# Dependencies of `io.spine.tools:psi-java:2.0.0-SNAPSHOT.460`
 
 ## Runtime
 1.  **Group** : be.cyberelf.nanoxml. **Name** : nanoxml. **Version** : 2.2.3.
@@ -18738,6 +18738,6 @@ This report was generated on **Tue Nov 03 02:04:37 WET 2026** using
 
 The dependencies distributed under several licenses, are used according their commercial-use-friendly license.
 
-This report was generated on **Tue Nov 03 02:04:37 WET 2026** using 
+This report was generated on **Tue Nov 03 21:49:47 WET 2026** using 
 [Gradle-License-Report plugin](https://github.com/jk1/Gradle-License-Report) by Evgeny Naumenko, licensed under 
 [Apache 2.0 License](https://github.com/jk1/Gradle-License-Report/blob/master/LICENSE).
\ No newline at end of file
diff --git a/docs/dependencies/pom.xml b/docs/dependencies/pom.xml
index bbb31acf6..3dc21609b 100644
--- a/docs/dependencies/pom.xml
+++ b/docs/dependencies/pom.xml
@@ -10,7 +10,7 @@ all modules and does not describe the project structure per-subproject.
  -->
 <groupId>io.spine.tools</groupId>
 <artifactId>tool-base</artifactId>
-<version>2.0.0-SNAPSHOT.451</version>
+<version>2.0.0-SNAPSHOT.460</version>
 
 <inceptionYear>2015</inceptionYear>
 
diff --git a/plugin-testlib/build.gradle.kts b/plugin-testlib/build.gradle.kts
index 607796b5e..db1e1d329 100644
--- a/plugin-testlib/build.gradle.kts
+++ b/plugin-testlib/build.gradle.kts
@@ -1,36 +1,29 @@
 /*
- * Copyright 2025, TeamDev. All rights reserved.
+ * Copyright 2026 CodeMatters, Lda.
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
  *
  * https://www.apache.org/licenses/LICENSE-2.0
  *
- * Redistribution and use in source and/or binary forms, with or without
- * modification, must retain the above copyright notice and the following
- * disclaimer.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
  */
 
 import io.spine.dependency.local.TestLib
 import io.spine.dependency.test.JUnit
+import io.spine.gradle.testing.enableTestKitCoverage
 
 plugins {
     module
 }
 
+// Credit coverage of the code executed in TestKit worker JVMs by the
+// `GradleProjectSpec` tests. See `io.spine.gradle.testing.enableTestKitCoverage`.
+enableTestKitCoverage()
+
 dependencies {
     api(gradleApi())
     api(gradleTestKit())
diff --git a/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/Gradle.kt b/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/Gradle.kt
index a36003572..9f09c747b 100644
--- a/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/Gradle.kt
+++ b/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/Gradle.kt
@@ -1,27 +1,15 @@
 /*
- * Copyright 2026, TeamDev. All rights reserved.
+ * Copyright 2026 CodeMatters, Lda.
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
  *
  * https://www.apache.org/licenses/LICENSE-2.0
  *
- * Redistribution and use in source and/or binary forms, with or without
- * modification, must retain the above copyright notice and the following
- * disclaimer.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
  */
 
 package io.spine.tools.gradle.testing
@@ -94,8 +82,7 @@ public fun runGradleBuild(
     val runner = GradleRunner.create()
         .withProjectDir(projectDir)
         .withPluginClasspath()
-        .withArguments(arguments)
-    runner.enableTestKitCoverage()
+        .withArguments(arguments.withTestKitCoverage())
     stdOutput?.let {
         runner.forwardStdOutput(it)
     }
diff --git a/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/GradleProject.kt b/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/GradleProject.kt
index ff007dc85..730a25e17 100644
--- a/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/GradleProject.kt
+++ b/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/GradleProject.kt
@@ -1,27 +1,15 @@
 /*
- * Copyright 2026, TeamDev. All rights reserved.
+ * Copyright 2026 CodeMatters, Lda.
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
  *
  * https://www.apache.org/licenses/LICENSE-2.0
  *
- * Redistribution and use in source and/or binary forms, with or without
- * modification, must retain the above copyright notice and the following
- * disclaimer.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
  */
 
 package io.spine.tools.gradle.testing
@@ -48,23 +36,25 @@ import org.gradle.testkit.runner.UnexpectedBuildFailure
  * Plugin code exercised through Gradle TestKit runs in a separate worker JVM, which
  * JaCoCo/Kover do not instrument by default, so that out-of-process execution is
  * otherwise not credited to coverage. This library attaches the JaCoCo agent to the
- * worker JVM automatically — for projects run via this class as well as via
- * [runGradleBuild] — but only when the test JVM is started with two system
- * properties, which the consuming build is responsible for setting:
+ * worker JVM automatically — for builds started by [executeTask] and [executeAndFail]
+ * of this class as well as by [runGradleBuild] — but only when the test JVM is started
+ * with two system properties, which the consuming build is responsible for setting:
  *
- *  - `io.spine.tools.gradle.testkit.coverage.agent` — the absolute path to the
- *    standalone JaCoCo agent JAR, that is, the artifact
- *    `org.jacoco:org.jacoco.agent:<version>:runtime`.
- *  - `io.spine.tools.gradle.testkit.coverage.execDir` — the directory into which the
- *    worker should write its execution data. The harness creates a single
- *    per-module `testkit.exec` file inside it.
+ *  - [TestKitCoverage.AGENT_PROPERTY] — the absolute path to the standalone JaCoCo
+ *    agent JAR, that is, the artifact `org.jacoco:org.jacoco.agent:<version>:runtime`.
+ *  - [TestKitCoverage.EXEC_DIR_PROPERTY] — the directory into which the worker should
+ *    write its execution data. The harness creates a single per-module `testkit.exec`
+ *    file inside it.
  *
- * When the properties are absent the harness is a no-op, so ordinary runs and
- * consumers that do not opt in are unaffected.
+ * When either of these properties is absent, the harness is a no-op, so ordinary
+ * runs and consumers that do not opt in are unaffected. A build started from
+ * [runner] directly gets no agent.
  *
  * The snippet below is a self-contained Gradle (Kotlin DSL) setup that a module
  * running TestKit-based tests can copy into its `build.gradle.kts`. Pin the agent
- * to the same JaCoCo version your coverage tooling uses.
+ * to the same JaCoCo version your coverage tooling uses. The snippet spells out the
+ * property names held by [TestKitCoverage], because a build script does not see
+ * the classes of this library.
  *
  * ```kotlin
  * import java.util.concurrent.atomic.AtomicBoolean
@@ -116,6 +106,16 @@ import org.gradle.testkit.runner.UnexpectedBuildFailure
  * `config`'s `buildSrc`, and the produced files are merged into Kover reports by
  * `KoverConfig`. Consumers outside that setup can use the snippet above instead.
  *
+ * ## TestKit directory
+ *
+ * The TestKit directory is the Gradle user home of the worker builds. A project set
+ * up with [GradleProjectSetup.withSharedTestKitDirectory] uses the directory given
+ * there, or `caches/spine-testkit` under the Gradle user home if given none. Other
+ * builds started by this class and by [runGradleBuild] use the directory TestKit
+ * picks: the one named by Gradle's `org.gradle.testkit.dir` system property of the
+ * test JVM, or one under the temporary directory of the `Test` task without it.
+ * This choice is independent of the coverage setup above.
+ *
  * @see GradleProjectSetup
  */
 public class GradleProject internal constructor(setup: GradleProjectSetup) {
@@ -139,20 +139,17 @@ public class GradleProject internal constructor(setup: GradleProjectSetup) {
 
     /**
      * The runner for executing tasks.
+     *
+     * A build started from the runner directly, rather than by [executeTask] or
+     * [executeAndFail], runs without the TestKit coverage agent.
      */
     public val runner: GradleRunner by lazy {
         val runner = GradleRunner.create()
             .withProjectDir(setup.projectDir)
             .withDebug(setup.debug)
-        val sharedTestKitDir = if (setup.useSharedTestKit) {
-            RootProject.testKitTempDir().toFile().apply { mkdirs() }
-        } else {
-            null
-        }
-        if (sharedTestKitDir != null) {
-            runner.withTestKitDir(sharedTestKitDir)
+        setup.testKitDir()?.let { dir ->
+            runner.withTestKitDir(dir.apply { mkdirs() })
         }
-        runner.enableTestKitCoverage(sharedTestKitDir)
         runner
     }
 
@@ -264,7 +261,7 @@ public class GradleProject internal constructor(setup: GradleProjectSetup) {
 
     private fun prepareRun(taskName: TaskName): GradleRunner {
         val args = arguments.forTask(taskName)
-        return runner.withArguments(args)
+        return runner.withArguments(args.withTestKitCoverage())
     }
 
     /**
diff --git a/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/GradleProjectSetup.kt b/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/GradleProjectSetup.kt
index 98f42b346..391bc1ddf 100644
--- a/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/GradleProjectSetup.kt
+++ b/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/GradleProjectSetup.kt
@@ -1,28 +1,17 @@
 /*
- * Copyright 2022, TeamDev. All rights reserved.
+ * Copyright 2026 CodeMatters, Lda.
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
  *
- * http://www.apache.org/licenses/LICENSE-2.0
+ * https://www.apache.org/licenses/LICENSE-2.0
  *
- * Redistribution and use in source and/or binary forms, with or without
- * modification, must retain the above copyright notice and the following
- * disclaimer.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
  */
+
 package io.spine.tools.gradle.testing
 
 import io.spine.annotation.VisibleForTesting
@@ -93,10 +82,16 @@ public class GradleProjectSetup internal constructor(
     internal var debug = false
         private set
 
-    /** Whether a [shared Gradle TestKit folder][RootProject.testKitTempDir] should be used. */
+    /** Whether a [shared Gradle TestKit directory][withSharedTestKitDirectory] should be used. */
     internal var useSharedTestKit = false
         private set
 
+    /**
+     * The shared TestKit directory [given][withSharedTestKitDirectory] explicitly,
+     * or `null` if none was given.
+     */
+    private var sharedTestKitDir: File? = null
+
     /**
      * Determines whether the plugin under test classpath is defined and
      * should be added to the Gradle execution classpath.
@@ -364,17 +359,37 @@ public class GradleProjectSetup internal constructor(
     }
 
     /**
-     * Tells the TestKit runner to use a [single shared folder][RootProject.testKitTempDir]
-     * for all tests.
+     * Tells the TestKit runner to use a TestKit directory shared by the tests.
+     *
+     * The TestKit directory is the Gradle user home of the test builds. When it is
+     * shared, a build can reuse what earlier builds left there, such as Gradle's
+     * instrumented copies of the JARs on the classpath of the plugin under test.
+     * The directory is not deleted by `clean`.
      *
-     * The idea is that this folder is not deleted on `gradlew clean` phase,
-     * and therefore may be somewhat re-used to speed up the test execution.
+     * @param dir The directory to use. If `null`, the runner uses `caches/spine-testkit`
+     *   under the Gradle user home. The Gradle user home is looked up in the order
+     *   Gradle uses: the `gradle.user.home` system property of the test JVM, then the
+     *   `GRADLE_USER_HOME` environment variable, then `.gradle` in the home directory
+     *   of the user.
      */
-    public fun withSharedTestKitDirectory() : GradleProjectSetup {
+    @JvmOverloads
+    public fun withSharedTestKitDirectory(dir: File? = null): GradleProjectSetup {
         this.useSharedTestKit = true
+        this.sharedTestKitDir = dir
         return this
     }
 
+    /**
+     * Obtains the TestKit directory to give the runner, or `null` to leave the choice
+     * to TestKit.
+     */
+    internal fun testKitDir(): File? =
+        if (useSharedTestKit) {
+            sharedTestKitDir ?: defaultSharedTestKitDir()
+        } else {
+            null
+        }
+
     /**
      * Creates a new project on the file system.
      */
diff --git a/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/GradleUserHome.kt b/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/GradleUserHome.kt
new file mode 100644
index 000000000..5ce961b43
--- /dev/null
+++ b/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/GradleUserHome.kt
@@ -0,0 +1,104 @@
+/*
+ * Copyright 2026 CodeMatters, Lda.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
+ */
+
+package io.spine.tools.gradle.testing
+
+import java.io.File
+
+/**
+ * Returns the TestKit directory that a project set up with
+ * [GradleProjectSetup.withSharedTestKitDirectory] uses when given none:
+ * `caches/spine-testkit` under the [Gradle user home][gradleUserHome].
+ *
+ * @param property Returns the value of the system property with the given name.
+ * @param environment Returns the value of the environment variable with the given name.
+ */
+internal fun defaultSharedTestKitDir(
+    property: (String) -> String? = System::getProperty,
+    environment: (String) -> String? = System::getenv
+): File = gradleUserHome(property, environment)
+    .resolve(CACHES_DIR)
+    .resolve(SHARED_TESTKIT_DIR)
+
+/**
+ * Returns the Gradle user home, looked up in the order Gradle uses:
+ *
+ *  1. The `gradle.user.home` system property.
+ *  2. The `GRADLE_USER_HOME` environment variable.
+ *  3. The `.gradle` directory in the home directory of the user (`user.home`).
+ *
+ * A blank value counts as not set. The path is composed with [File], so it gets
+ * the separators of the platform, and a Windows path such as `D:\a\.gradle` is
+ * kept as given.
+ *
+ * The lookup runs in the test JVM. That JVM does not see a Gradle user home passed
+ * to the outer build only with the `-g` option, so its result is then the default.
+ *
+ * @param property Returns the value of the system property with the given name.
+ * @param environment Returns the value of the environment variable with the given name.
+ */
+internal fun gradleUserHome(
+    property: (String) -> String?,
+    environment: (String) -> String?
+): File {
+    val given = property(GRADLE_USER_HOME_PROPERTY).nonBlank()
+        ?: environment(GRADLE_USER_HOME_VARIABLE).nonBlank()
+    if (given != null) {
+        return File(given)
+    }
+    val userHome = checkNotNull(property(USER_HOME_PROPERTY)) {
+        "The `$USER_HOME_PROPERTY` system property is not set."
+    }
+    return File(userHome, GRADLE_DIR)
+}
+
+private fun String?.nonBlank(): String? = this?.takeIf { it.isNotBlank() }
+
+/**
+ * The name of the system property with which Gradle can be given its user home,
+ * as by `-Dgradle.user.home=<dir>`.
+ */
+private const val GRADLE_USER_HOME_PROPERTY: String = "gradle.user.home"
+
+/**
+ * The name of the environment variable with which Gradle can be given its user home.
+ *
+ * It is consulted when the [GRADLE_USER_HOME_PROPERTY] system property is not set.
+ */
+private const val GRADLE_USER_HOME_VARIABLE: String = "GRADLE_USER_HOME"
+
+/**
+ * The name of the standard Java system property carrying the home directory of
+ * the user, which holds the [default Gradle user home][GRADLE_DIR].
+ */
+private const val USER_HOME_PROPERTY: String = "user.home"
+
+/**
+ * The name of the directory, in the home directory of the user, that serves as
+ * the Gradle user home when neither [GRADLE_USER_HOME_PROPERTY] nor
+ * [GRADLE_USER_HOME_VARIABLE] names another one.
+ */
+private const val GRADLE_DIR: String = ".gradle"
+
+/**
+ * The name of the directory under the Gradle user home that holds the caches
+ * of Gradle and the [shared TestKit directory][SHARED_TESTKIT_DIR].
+ */
+private const val CACHES_DIR: String = "caches"
+
+/**
+ * The name of the TestKit directory shared by the test builds, placed in
+ * the [caches directory][CACHES_DIR] of the Gradle user home.
+ */
+private const val SHARED_TESTKIT_DIR: String = "spine-testkit"
diff --git a/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/RootProject.kt b/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/RootProject.kt
index de5138f3c..26dd32672 100644
--- a/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/RootProject.kt
+++ b/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/RootProject.kt
@@ -1,28 +1,17 @@
 /*
- * Copyright 2022, TeamDev. All rights reserved.
+ * Copyright 2026 CodeMatters, Lda.
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
  *
- * http://www.apache.org/licenses/LICENSE-2.0
+ * https://www.apache.org/licenses/LICENSE-2.0
  *
- * Redistribution and use in source and/or binary forms, with or without
- * modification, must retain the above copyright notice and the following
- * disclaimer.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
  */
+
 package io.spine.tools.gradle.testing
 
 import java.io.File
@@ -80,16 +69,4 @@ internal object RootProject {
     fun dir(): File {
         return path().toFile()
     }
-
-    /**
-     * Returns a path to a conventionally established temp directory named `.gradle-test-kit`,
-     * for Gradle TestKit runners.
-     *
-     * It may be used to configure TestKit runners, so that just a single folder
-     * is created for all integration tests.
-     */
-    @JvmStatic
-    fun testKitTempDir() : Path {
-        return path().resolve(".gradle-test-kit")
-    }
 }
diff --git a/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/TestKitCoverage.kt b/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/TestKitCoverage.kt
index 98fb482e9..95f1c3550 100644
--- a/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/TestKitCoverage.kt
+++ b/plugin-testlib/src/main/kotlin/io/spine/tools/gradle/testing/TestKitCoverage.kt
@@ -1,105 +1,111 @@
 /*
- * Copyright 2026, TeamDev. All rights reserved.
+ * Copyright 2026 CodeMatters, Lda.
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
  *
  * https://www.apache.org/licenses/LICENSE-2.0
  *
- * Redistribution and use in source and/or binary forms, with or without
- * modification, must retain the above copyright notice and the following
- * disclaimer.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
  */
 
 package io.spine.tools.gradle.testing
 
 import java.io.File
-import org.gradle.testkit.runner.GradleRunner
 
 /**
- * Attaches the JaCoCo coverage agent to the worker JVM spawned by this runner,
- * so that plugin code executed out-of-process via TestKit is credited to coverage.
- *
- * Does nothing unless the test JVM was started with the [AGENT_PROPERTY] and
- * [EXEC_DIR_PROPERTY] system properties. This keeps the harness a no-op for
- * ordinary runs and for consumers that do not opt in.
- *
- * Supplying those two properties on the test JVM is the responsibility of the
- * consuming build. Consumer-facing setup instructions, including a copy-paste
- * Gradle recipe, live in the [GradleProject] KDoc (this function is `internal`,
- * so its own KDoc is not part of the published API documentation).
+ * The names of the system properties with which the consuming build enables
+ * the coverage of Gradle TestKit worker JVMs.
  *
- * When enabled, the method writes a `gradle.properties` carrying a `-javaagent:…`
- * argument into the TestKit directory (the Gradle user home of the worker build),
- * and points the runner at that directory. The JaCoCo agent appends to a single
- * per-module [execution-data file][EXEC_FILE]; on worker daemon shutdown — which
- * happens after the tests complete and before the coverage report task runs — the
- * data is flushed to disk.
+ * The consuming build sets them on the test JVM, as described in [GradleProject].
  *
- * @param preferredTestKitDir The TestKit directory the caller already intends to
- *   use (e.g. a [shared one][GradleProjectSetup.withSharedTestKitDirectory]), or
- *   `null` to let this method pick the per-module [TESTKIT_HOME_DIR].
+ * The property names are part of the contract with consuming builds and must not
+ * change: a build sets the properties by name, and is versioned independently of
+ * this library.
  */
-internal fun GradleRunner.enableTestKitCoverage(preferredTestKitDir: File? = null) {
-    val agentJar = System.getProperty(AGENT_PROPERTY) ?: return
-    val execDirPath = System.getProperty(EXEC_DIR_PROPERTY) ?: return
+public object TestKitCoverage {
 
-    val execDir = File(execDirPath).apply { mkdirs() }
-    val execFile = File(execDir, EXEC_FILE)
-    val testKitDir = (preferredTestKitDir ?: File(execDir.parentFile, TESTKIT_HOME_DIR))
-        .apply { mkdirs() }
+    // The `io.spine.gradle.testing.enableTestKitCoverage` extension in `config`'s
+    // `buildSrc` sets these properties. It repeats the names, because it does not
+    // depend on this library.
 
-    val jvmArg = "-javaagent:${agentJar.forProperties()}=" +
-            "destfile=${execFile.invariantSeparatorsPath}," +
-            "append=true,dumponexit=true,output=file,jmx=false"
-    File(testKitDir, "gradle.properties")
-        .writeText("org.gradle.jvmargs=$jvmArg\n")
+    /**
+     * The prefix shared by the names of the properties.
+     */
+    private const val PREFIX: String = "io.spine.tools.gradle.testkit.coverage"
 
-    withTestKitDir(testKitDir)
-}
+    /**
+     * The name of the system property carrying the absolute path to the JaCoCo
+     * agent JAR to attach to a Gradle TestKit worker JVM. The JAR is the artifact
+     * `org.jacoco:org.jacoco.agent:<version>:runtime`.
+     */
+    public const val AGENT_PROPERTY: String = "$PREFIX.agent"
 
-/**
- * Normalizes a file-system path for safe inclusion into a `*.properties` file
- * by using forward slashes regardless of the host platform.
- */
-private fun String.forProperties(): String = File(this).invariantSeparatorsPath
+    /**
+     * The name of the system property carrying the absolute path to the directory
+     * where the TestKit worker should write its JaCoCo execution data.
+     */
+    public const val EXEC_DIR_PROPERTY: String = "$PREFIX.execDir"
+}
 
 /**
- * The name of the system property carrying the absolute path to the JaCoCo
- * agent JAR to attach to a Gradle TestKit worker JVM.
+ * Returns these arguments with the `-Dorg.gradle.jvmargs` argument that attaches
+ * the JaCoCo agent to the worker JVM appended, or the same arguments when TestKit
+ * coverage is not enabled.
+ *
+ * TestKit coverage is enabled when the test JVM was started with the
+ * [TestKitCoverage.AGENT_PROPERTY] and [TestKitCoverage.EXEC_DIR_PROPERTY] system
+ * properties. Without them, the harness is a no-op for ordinary runs and for
+ * consumers that do not opt in. Supplying the properties is the responsibility of
+ * the consuming build; the setup instructions live in the [GradleProject] KDoc.
+ *
+ * The agent appends to a single per-module [execution-data file][EXEC_FILE]; on
+ * worker daemon shutdown — which happens after the tests complete and before the
+ * coverage report task runs — the data is flushed to disk.
  *
- * The consuming build is expected to set this property on the test JVM. Within
- * the SpineEventEngine organisation it is set by the
- * `io.spine.gradle.testing.enableTestKitCoverage` extension in `config`'s
- * `buildSrc`, where the constant is duplicated (the `buildSrc` and the production
- * source sets cannot share code). Keep the two values in sync.
+ * The agent is passed on the command line rather than in a `gradle.properties` file
+ * in the TestKit directory, so that coverage does not depend on which TestKit
+ * directory the runner uses. The argument replaces the `org.gradle.jvmargs` the
+ * worker build would use otherwise, such as the one of the `gradle.properties` of
+ * the test project, or one passed earlier in these arguments.
  */
-private const val AGENT_PROPERTY: String =
-    "io.spine.tools.gradle.testkit.coverage.agent"
+internal fun List<String>.withTestKitCoverage(): List<String> {
+    val coverage = CoverageSetup.fromSystemProperties() ?: return this
+    val execFile = File(coverage.execDir, EXEC_FILE)
+    // Forward slashes work on every platform and need no escaping.
+    val jvmArg = "-javaagent:${coverage.agentJar.invariantSeparatorsPath}=" +
+            "destfile=${execFile.invariantSeparatorsPath}," +
+            "append=true,dumponexit=true,output=file,jmx=false"
+    return this + "-Dorg.gradle.jvmargs=$jvmArg"
+}
 
 /**
- * The name of the system property carrying the absolute path to the directory
- * where the TestKit worker should write its JaCoCo execution data.
+ * The TestKit coverage setup the consuming build passed to this test JVM.
  *
- * Set by the consuming build on the test JVM. Within the SpineEventEngine
- * organisation this is done by the `io.spine.gradle.testing.enableTestKitCoverage`
- * extension in `config`'s `buildSrc`; keep the two values in sync.
+ * @property agentJar The JaCoCo agent JAR.
+ * @property execDir The directory for the execution data of the worker JVMs.
  */
-private const val EXEC_DIR_PROPERTY: String =
-    "io.spine.tools.gradle.testkit.coverage.execDir"
+private class CoverageSetup(val agentJar: File, val execDir: File) {
+
+    companion object {
+
+        /**
+         * Reads the setup from the system properties of this test JVM,
+         * or returns `null` when TestKit coverage is not enabled for it.
+         */
+        fun fromSystemProperties(): CoverageSetup? {
+            val agentJar = System.getProperty(TestKitCoverage.AGENT_PROPERTY)
+            val execDir = System.getProperty(TestKitCoverage.EXEC_DIR_PROPERTY)
+            if (agentJar == null || execDir == null) {
+                return null
+            }
+            return CoverageSetup(File(agentJar), File(execDir))
+        }
+    }
+}
 
 /**
  * The name of the JaCoCo execution-data file written by TestKit workers.
@@ -110,13 +116,3 @@ private const val EXEC_DIR_PROPERTY: String =
  * into the Kover reports.
  */
 private const val EXEC_FILE: String = "testkit.exec"
-
-/**
- * The name of the directory, placed next to the [execution-data directory][EXEC_DIR_PROPERTY],
- * that serves as the dedicated Gradle user home (the TestKit directory) for the
- * coverage-enabled worker builds.
- *
- * Reusing one TestKit directory per module lets a single TestKit daemon serve all
- * the test cases, keeping the agent attached with a stable `destfile`.
- */
-private const val TESTKIT_HOME_DIR: String = "testkit-home"
diff --git a/plugin-testlib/src/test/kotlin/io/spine/tools/gradle/testing/GradleProjectSetupSpec.kt b/plugin-testlib/src/test/kotlin/io/spine/tools/gradle/testing/GradleProjectSetupSpec.kt
index 458aa35c8..36f2d7a66 100644
--- a/plugin-testlib/src/test/kotlin/io/spine/tools/gradle/testing/GradleProjectSetupSpec.kt
+++ b/plugin-testlib/src/test/kotlin/io/spine/tools/gradle/testing/GradleProjectSetupSpec.kt
@@ -1,27 +1,15 @@
 /*
- * Copyright 2026, TeamDev. All rights reserved.
+ * Copyright 2026 CodeMatters, Lda.
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
  *
  * https://www.apache.org/licenses/LICENSE-2.0
  *
- * Redistribution and use in source and/or binary forms, with or without
- * modification, must retain the above copyright notice and the following
- * disclaimer.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
  */
 
 package io.spine.tools.gradle.testing
@@ -114,6 +102,29 @@ class GradleProjectSetupSpec {
         setup.useSharedTestKit shouldBe true
     }
 
+    @Nested
+    inner class `choose the TestKit directory` {
+
+        @Test
+        fun `leaving it to TestKit by default`() {
+            setup.testKitDir() shouldBe null
+        }
+
+        @Test
+        fun `taking the one given`(@TempDir dir: File) {
+            setup.withSharedTestKitDirectory(dir)
+
+            setup.testKitDir() shouldBe dir
+        }
+
+        @Test
+        fun `taking the shared one under the Gradle user home when given none`() {
+            setup.withSharedTestKitDirectory()
+
+            setup.testKitDir() shouldBe defaultSharedTestKitDir()
+        }
+    }
+
     @Test
     fun `copy 'buildSrc' without caching`() {
         setup.copyBuildSrc(cachingEnabled = false)
diff --git a/plugin-testlib/src/test/kotlin/io/spine/tools/gradle/testing/GradleUserHomeSpec.kt b/plugin-testlib/src/test/kotlin/io/spine/tools/gradle/testing/GradleUserHomeSpec.kt
new file mode 100644
index 000000000..48f53ab6e
--- /dev/null
+++ b/plugin-testlib/src/test/kotlin/io/spine/tools/gradle/testing/GradleUserHomeSpec.kt
@@ -0,0 +1,121 @@
+/*
+ * Copyright 2026 CodeMatters, Lda.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
+ */
+
+package io.spine.tools.gradle.testing
+
+import io.kotest.matchers.shouldBe
+import io.kotest.matchers.string.shouldContain
+import java.io.File
+import org.junit.jupiter.api.DisplayName
+import org.junit.jupiter.api.Nested
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertThrows
+import org.junit.jupiter.api.condition.EnabledOnOs
+import org.junit.jupiter.api.condition.OS
+
+@DisplayName("Gradle user home lookup should")
+internal class GradleUserHomeSpec {
+
+    @Test
+    fun `prefer the system property of the Gradle user home`() {
+        val home = gradleUserHome(
+            systemProperties("gradle.user.home" to "/opt/gradle", "user.home" to "/home/me"),
+            environment("GRADLE_USER_HOME" to "/var/gradle")
+        )
+
+        home shouldBe File("/opt/gradle")
+    }
+
+    @Test
+    fun `use the 'GRADLE_USER_HOME' environment variable when the property is not set`() {
+        val home = gradleUserHome(
+            systemProperties("user.home" to "/home/me"),
+            environment("GRADLE_USER_HOME" to "/var/gradle")
+        )
+
+        home shouldBe File("/var/gradle")
+    }
+
+    @Test
+    fun `default to the dot-gradle directory in the home directory of the user`() {
+        val home = gradleUserHome(systemProperties("user.home" to "/home/me"), environment())
+
+        home shouldBe File("/home/me", ".gradle")
+    }
+
+    @Test
+    fun `treat blank values as not set`() {
+        val home = gradleUserHome(
+            systemProperties("gradle.user.home" to " ", "user.home" to "/home/me"),
+            environment("GRADLE_USER_HOME" to "")
+        )
+
+        home shouldBe File("/home/me", ".gradle")
+    }
+
+    @Test
+    fun `fail when the home directory of the user is not known`() {
+        val error = assertThrows<IllegalStateException> {
+            gradleUserHome(systemProperties(), environment())
+        }
+
+        error.message shouldContain "user.home"
+    }
+
+    @Test
+    fun `put the shared TestKit directory under 'caches' of the Gradle user home`() {
+        val dir = defaultSharedTestKitDir(
+            systemProperties("user.home" to "/home/me"),
+            environment("GRADLE_USER_HOME" to "/var/gradle")
+        )
+
+        dir shouldBe File("/var/gradle/caches/spine-testkit")
+    }
+
+    @Nested
+    @EnabledOnOs(OS.WINDOWS)
+    inner class `keep a Windows path` {
+
+        @Test
+        fun `given with backslashes`() {
+            val fromVariable = defaultSharedTestKitDir(
+                systemProperties("user.home" to "C:\\Users\\runneradmin"),
+                environment("GRADLE_USER_HOME" to "D:\\a\\.gradle")
+            )
+            val fromUserHome = defaultSharedTestKitDir(
+                systemProperties("user.home" to "C:\\Users\\runneradmin"),
+                environment()
+            )
+
+            fromVariable.path shouldBe "D:\\a\\.gradle\\caches\\spine-testkit"
+            fromUserHome.path shouldBe "C:\\Users\\runneradmin\\.gradle\\caches\\spine-testkit"
+        }
+
+        @Test
+        fun `given with forward slashes`() {
+            val dir = defaultSharedTestKitDir(
+                systemProperties("user.home" to "C:\\Users\\runneradmin"),
+                environment("GRADLE_USER_HOME" to "D:/a/.gradle")
+            )
+
+            dir.path shouldBe "D:\\a\\.gradle\\caches\\spine-testkit"
+        }
+    }
+}
+
+private fun systemProperties(vararg values: Pair<String, String>): (String) -> String? =
+    mapOf(*values)::get
+
+private fun environment(vararg values: Pair<String, String>): (String) -> String? =
+    mapOf(*values)::get
diff --git a/plugin-testlib/src/test/kotlin/io/spine/tools/gradle/testing/RootProjectSpec.kt b/plugin-testlib/src/test/kotlin/io/spine/tools/gradle/testing/RootProjectSpec.kt
index d439fe424..065e9101f 100644
--- a/plugin-testlib/src/test/kotlin/io/spine/tools/gradle/testing/RootProjectSpec.kt
+++ b/plugin-testlib/src/test/kotlin/io/spine/tools/gradle/testing/RootProjectSpec.kt
@@ -1,27 +1,15 @@
 /*
- * Copyright 2026, TeamDev. All rights reserved.
+ * Copyright 2026 CodeMatters, Lda.
  *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
  *
  * https://www.apache.org/licenses/LICENSE-2.0
  *
- * Redistribution and use in source and/or binary forms, with or without
- * modification, must retain the above copyright notice and the following
- * disclaimer.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
  */
 
 package io.spine.tools.gradle.testing
@@ -37,11 +25,4 @@ class RootProjectSpec {
     fun `locate the project root`() {
         RootProject.dir().exists() shouldBe true
     }
-
-    @Test
-    fun `provide the shared TestKit temp directory under the project root`() {
-        val testKitDir = RootProject.testKitTempDir()
-        testKitDir.startsWith(RootProject.path()) shouldBe true
-        testKitDir.fileName.toString() shouldBe ".gradle-test-kit"
-    }
 }
diff --git a/plugin-testlib/src/test/kotlin/io/spine/tools/gradle/testing/TestKitCoverageSpec.kt b/plugin-testlib/src/test/kotlin/io/spine/tools/gradle/testing/TestKitCoverageSpec.kt
new file mode 100644
index 000000000..fa9402d8f
--- /dev/null
+++ b/plugin-testlib/src/test/kotlin/io/spine/tools/gradle/testing/TestKitCoverageSpec.kt
@@ -0,0 +1,98 @@
+/*
+ * Copyright 2026 CodeMatters, Lda.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
+ */
+
+package io.spine.tools.gradle.testing
+
+import io.kotest.matchers.shouldBe
+import io.spine.tools.gradle.testing.TestKitCoverage.AGENT_PROPERTY
+import io.spine.tools.gradle.testing.TestKitCoverage.EXEC_DIR_PROPERTY
+import java.io.File
+import org.junit.jupiter.api.AfterEach
+import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.DisplayName
+import org.junit.jupiter.api.Nested
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.io.TempDir
+
+@DisplayName("TestKit coverage harness should")
+internal class TestKitCoverageSpec {
+
+    private val savedProperties = mutableMapOf<String, String?>()
+
+    @BeforeEach
+    fun clearProperties() {
+        COVERAGE_PROPERTIES.forEach { name ->
+            savedProperties[name] = System.getProperty(name)
+            System.clearProperty(name)
+        }
+    }
+
+    @AfterEach
+    fun restoreProperties() {
+        savedProperties.forEach { (name, value) ->
+            if (value == null) {
+                System.clearProperty(name)
+            } else {
+                System.setProperty(name, value)
+            }
+        }
+    }
+
+    @Test
+    fun `leave the arguments intact when coverage is not enabled`() {
+        val args = listOf("build")
+
+        args.withTestKitCoverage() shouldBe args
+    }
+
+    @Test
+    fun `stay disabled when only the agent property is set`(@TempDir dir: File) {
+        System.setProperty(AGENT_PROPERTY, dir.resolve("agent.jar").path)
+        val args = listOf("build")
+
+        args.withTestKitCoverage() shouldBe args
+    }
+
+    @Nested
+    inner class `when coverage is enabled` {
+
+        @TempDir
+        lateinit var dir: File
+
+        private val agentJar by lazy { dir.resolve("jacoco/agent.jar") }
+        private val execDir by lazy { dir.resolve("build/jacoco-testkit") }
+
+        @BeforeEach
+        fun enableCoverage() {
+            System.setProperty(AGENT_PROPERTY, agentJar.path)
+            System.setProperty(EXEC_DIR_PROPERTY, execDir.path)
+        }
+
+        @Test
+        fun `append the argument that attaches the agent to the worker JVM`() {
+            val args = listOf("build", "--stacktrace").withTestKitCoverage()
+
+            val execFile = execDir.resolve("testkit.exec")
+            args shouldBe listOf(
+                "build",
+                "--stacktrace",
+                "-Dorg.gradle.jvmargs=-javaagent:${agentJar.invariantSeparatorsPath}=" +
+                        "destfile=${execFile.invariantSeparatorsPath}," +
+                        "append=true,dumponexit=true,output=file,jmx=false"
+            )
+        }
+    }
+}
+
+private val COVERAGE_PROPERTIES = listOf(AGENT_PROPERTY, EXEC_DIR_PROPERTY)
diff --git a/version.gradle.kts b/version.gradle.kts
index 0faf741b6..bb97fa199 100644
--- a/version.gradle.kts
+++ b/version.gradle.kts
@@ -12,4 +12,4 @@
  * and limitations under the License.
  */
 
-extra.set("versionToPublish", "2.0.0-SNAPSHOT.451")
+extra.set("versionToPublish", "2.0.0-SNAPSHOT.460")