Add CodeCov

.github/workflows/coverage.yml

@@ -0,0 +1,56 @@
+name: Coverage
+
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  coverage:
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v7
+        with:
+          fetch-depth: 0
+
+      - name: Set Up Java 17 for Compatibility Tests
+        uses: actions/setup-java@v5
+        with:
+          distribution: temurin
+          java-version: 17
+
+      - name: Save Java 17 Toolchain
+        run: echo "EMBED_CODE_JAVA_17_HOME=$JAVA_HOME" >> "$GITHUB_ENV"
+
+      - name: Set Up Java 25
+        uses: actions/setup-java@v5
+        with:
+          distribution: temurin
+          java-version: 25
+
+      - name: Set Up Gradle
+        uses: gradle/actions/setup-gradle@v6
+
+      - name: Generate Test Coverage
+        run: >-
+          ./gradlew
+          -Dorg.gradle.java.installations.paths="$EMBED_CODE_JAVA_17_HOME"
+          --no-configuration-cache
+          :gradle-plugin:jacocoTestReport
+
+      - name: Upload Coverage
+        uses: codecov/codecov-action@v7
+        with:
+          files: ./gradle-plugin/build/reports/jacoco/test/jacocoTestReport.xml
+          token: ${{ secrets.CODECOV_TOKEN }}

PROJECT.md

@@ -38,6 +38,8 @@ Embed Code configuration file and do not need to install the executable or Kotli
 - `config/detekt/`: project-specific Detekt rules and the baseline for existing findings.
 - `scripts/check_agent_config.py` and `scripts/tests/`: deterministic validation and tests.
 - `.github/workflows/check.yml`: agent configuration and Ubuntu and Windows build verification.
+- `.github/workflows/coverage.yml`: JaCoCo report generation and Codecov upload, using the patch
+  target defined in `codecov.yml`.
 - `.claude/commands/`: thin Claude slash-command entry points for deliberate workflows.
 - `.agents/guidelines/`: shared writing, English-language, and project-ownership rules.
 - `.agents/skills/`: repository engineering, test, writing, review, and security workflows.
@@ -87,6 +89,10 @@ version numbers into agent guidance where a durable source path is sufficient.
 - Keep tests offline with deterministic fixtures, temporary directories, and loopback HTTP servers.
 - Use `./gradlew test` for unit tests, `./gradlew functionalTest` for TestKit tests, and
   `./gradlew check` for both plus plugin validation.
+- Use `./gradlew --no-configuration-cache :gradle-plugin:jacocoTestReport` to combine unit and
+  TestKit coverage into Codecov XML. The coverage-only TestKit task instruments forked builds and
+  does not support the configuration cache; the ordinary functional suite still verifies
+  configuration-cache reuse.
 - Use `./gradlew :buildSrc:check` for the build-logic tests and Detekt analysis. `buildSrc` is a
   separate build, so the root `check` task does not reach them; CI runs the task explicitly.
 - Use `./gradlew generateDependencyReports` after changing dependencies or the plugin version.

README.md

@@ -1,4 +1,5 @@
 [![Build on Ubuntu and Windows][build-badge]][gh-actions]
+[![Codecov][coverage-badge]][codecov]
 [![license](https://img.shields.io/badge/license-Apache%20License%202.0-blue.svg?style=flat)](http://www.apache.org/licenses/LICENSE-2.0)
 
 # Embed Code Gradle plugin
@@ -178,5 +179,7 @@ consuming project's `settings.gradle.kts`. Adding it only to the regular
 The plugin is available under the [Apache License 2.0](LICENSE).
 
 [build-badge]: https://github.com/SpineEventEngine/embed-code-gradle-plugin/actions/workflows/check.yml/badge.svg
+[codecov]: https://codecov.io/gh/SpineEventEngine/embed-code-gradle-plugin
+[coverage-badge]: https://codecov.io/gh/SpineEventEngine/embed-code-gradle-plugin/graph/badge.svg
 [embed-code]: https://github.com/SpineEventEngine/embed-code-go
 [gh-actions]: https://github.com/SpineEventEngine/embed-code-gradle-plugin/actions

codecov.yml

@@ -0,0 +1,10 @@
+coverage:
+  status:
+    project:
+      default:
+        informational: true
+    patch:
+      default:
+        target: 90%
+        threshold: 0%
+        only_pulls: true

gradle-plugin/build.gradle.kts

@@ -34,14 +34,17 @@ import io.spine.embedcode.gradle.report.DependencyMarkdownReportRenderer
 import io.spine.embedcode.gradle.report.GenerateDependencyPom
 import io.spine.embedcode.gradle.report.UpdateDependencyReports
 import org.apache.tools.ant.filters.ReplaceTokens
+import org.gradle.api.Action
 import org.gradle.api.publish.maven.MavenPublication
 import org.gradle.api.tasks.Sync
 import org.gradle.plugin.compatibility.compatibility
+import org.gradle.testing.jacoco.plugins.JacocoTaskExtension
 
 plugins {
     id("jvm-module")
     id("dokka-configuration")
     `java-gradle-plugin`
+    jacoco
     `maven-publish`
 }
 
@@ -98,9 +101,7 @@ configurations[functionalTestSourceSet.runtimeOnlyConfigurationName].extendsFrom
     configurations.testRuntimeOnly.get(),
 )
 
-val functionalTest = tasks.register<Test>("functionalTest") {
-    description = "Runs TestKit functional tests."
-    group = LifecycleBasePlugin.VERIFICATION_GROUP
+val configureFunctionalTest = Action<Test> {
     testClassesDirs = functionalTestSourceSet.output.classesDirs
     classpath = functionalTestSourceSet.runtimeClasspath
     useJUnitPlatform()
@@ -113,10 +114,66 @@ val functionalTest = tasks.register<Test>("functionalTest") {
     shouldRunAfter(tasks.test)
 }
 
+val functionalTest = tasks.register<Test>("functionalTest") {
+    configureFunctionalTest.execute(this)
+    description = "Runs TestKit functional tests."
+    group = LifecycleBasePlugin.VERIFICATION_GROUP
+    extensions.configure<JacocoTaskExtension> {
+        isEnabled = false
+    }
+}
+
+val testKitCoverageData = layout.buildDirectory.file("jacoco/testKit.exec")
+val coverageFunctionalTest = tasks.register<Test>("coverageFunctionalTest") {
+    configureFunctionalTest.execute(this)
+    description = "Runs TestKit functional tests and collects plugin coverage."
+    group = LifecycleBasePlugin.VERIFICATION_GROUP
+    extensions.configure<JacocoTaskExtension> {
+        isEnabled = false
+        setDestinationFile(testKitCoverageData.map { file -> file.asFile })
+    }
+    outputs.file(testKitCoverageData)
+    notCompatibleWithConfigurationCache(
+        "JaCoCo coverage of forked TestKit builds requires execution-time agent paths.",
+    )
+    doFirst {
+        val coverageDataFile = testKitCoverageData.get().asFile
+        coverageDataFile.delete()
+        val jacocoExtension = extensions.getByType<JacocoTaskExtension>()
+        // TestKit daemons use another working directory, so JaCoCo needs an absolute destination.
+        val childJvmArgument =
+            Regex("""destfile=[^,]+""").replaceFirst(
+                jacocoExtension.asJvmArg,
+                Regex.escapeReplacement("destfile=${coverageDataFile.absolutePath}"),
+            )
+        systemProperty(
+            "io.spine.embedcode.gradle.testkit.coverage.jvm-argument",
+            childJvmArgument,
+        )
+    }
+}
+
 tasks.check {
     dependsOn(functionalTest)
 }
 
+tasks.jacocoTestReport {
+    dependsOn(tasks.test, coverageFunctionalTest)
+    executionData(
+        tasks.test.map { task ->
+            task.extensions.getByType<JacocoTaskExtension>().destinationFile
+        },
+        coverageFunctionalTest.map { task ->
+            task.extensions.getByType<JacocoTaskExtension>().destinationFile
+        },
+    )
+    reports {
+        xml.required.set(true)
+        html.required.set(false)
+        csv.required.set(false)
+    }
+}
+
 base {
     archivesName.set("embed-code-gradle-plugin")
 }