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[[test_kit]]
= Testing Build Logic with TestKit

The Gradle TestKit helps you functionally test Gradle plugins and build logic by executing real builds in an isolated temp project and asserting on their results.
You’ll typically pair TestKit with a test framework (JUnit or Spock) and a few small fixtures to generate test projects on the fly.
Over time, TestKit has focused on functional/black-box testing, and that remains its sweet spot.

[[sec:testkit_usage]]
== Using TestKit

Add TestKit to your test dependencies:

====
include::sample[dir="snippets/reference/plugin-development/junitQuickstart/kotlin",files="build.gradle.kts[tags=declare-gradle-testkit-dependency]"]
include::sample[dir="snippets/reference/plugin-development/junitQuickstart/groovy",files="build.gradle[tags=declare-gradle-testkit-dependency]"]
====

The `gradleTestKit()` encompasses the classes of the TestKit, as well as the <<tooling_api.adoc#embedding,Gradle Tooling API client>>.
It does not include a version of https://junit.org[JUnit], https://testng.org[TestNG], or any other test execution framework.
Such a dependency must be explicitly declared.

For JUnit 5:

====
include::sample[dir="snippets/reference/plugin-development/junitQuickstart/kotlin",files="build.gradle.kts[tags=declare-junit-dependency]"]
include::sample[dir="snippets/reference/plugin-development/junitQuickstart/groovy",files="build.gradle[tags=declare-junit-dependency]"]
====

[[sec:functional_testing_with_the_gradle_runner]]
== Functional testing with the Gradle runner

A modern way to organize plugin tests is to add a dedicated functional test suite using the JVM Test Suite plugin (added transitively by `java-gradle-plugin`).
This cleanly separates unit and functional tests and wires TestKit for you.

The link:{javadocPath}/org/gradle/testkit/runner/GradleRunner.html[`GradleRunner`] allows you to programmatically execute Gradle builds and inspect their results.

A test can create a minimal or contrived build (either programmatically or from a template) that exercises the logic under test.
The functional test then runs that build, potentially using different tasks, arguments, or Gradle versions, and verifies correctness by asserting any combination of the following:

* The build output
* The build's logging
* The tasks that executed and their outcomes (e.g., FAILED, UP-TO-DATE, FROM-CACHE)

After creating and configuring a runner instance, execute the build using link:{javadocPath}/org/gradle/testkit/runner/GradleRunner.html#build--[`GradleRunner.build()`] or link:{javadocPath}/org/gradle/testkit/runner/GradleRunner.html#buildAndFail--[`GradleRunner.buildAndFail()`], depending on whether the build is expected to succeed or fail.

The following demonstrates the usage of the Gradle runner in a Java JUnit test:

[source, java]
.BuildLogicFunctionalTest.java
----
include::{snippetsPath}/reference/plugin-development/junitQuickstart/common/src/test/java/org/gradle/sample/BuildLogicFunctionalTest.java[tag=functional-test-junit]
----

Any test framework can be used.

Because Gradle build scripts are often written in Groovy, many users find it productive to write functional tests in Groovy as well.
The https://spockframework.org[Spock] framework provides expressive assertions, data-driven tests, and powerful fixtures that work well with TestKit.
Similarly, Kotlin users often choose either JUnit Jupiter or https://kotest.io[Kotest] for a more idiomatic Kotlin testing experience.

The following demonstrates the usage of the Gradle runner in a Groovy Spock test:

[source, groovy]
.BuildLogicFunctionalTest.groovy
----
include::{snippetsPath}/reference/plugin-development/spockQuickstart/groovy/src/test/groovy/org/gradle/sample/BuildLogicFunctionalTest.groovy[tag=functional-test-spock]
----

When implementing more complex build logic (such as custom plugins or task types), you can package that logic into external classes and test them in isolation using "normal" unit tests.
Functional tests using TestKit then validate that the plugin behaves correctly when applied to a real Gradle build.

[[sub:test-kit-classpath-injection]]
== Getting the plugin-under-test into the test build

The `GradleRunner` uses the <<tooling_api.adoc#embedding,Tooling API>> to execute builds.
This means that builds run in a *separate* process from your tests.
As a result:

* The test build does not share the same classpath or classloaders as the test process.
* The code under test (for example, your plugin implementation) is **not** automatically visible to the build executed by `GradleRunner`.

[NOTE]
====
`GradleRunner` supports the same range of Gradle versions as the Tooling API.
The supported versions are defined in the <<tooling_api.adoc#sec:embedding_compatibility,compatibility matrix>>.

Builds with older Gradle versions *may* still work, but there are no guarantees.
====

To make your plugin (or other build logic under test) available to the test build, Gradle provides a conventional mechanism to inject the *plugin-under-test* onto the classpath used by `GradleRunner`.

[[sub:test-kit-automatic-classpath-injection]]
=== Automatic injection with the Java Gradle Plugin Development plugin

The <<java_gradle_plugin.adoc#java_gradle_plugin,Java Gradle Plugin Development plugin>> provides built-in integration with TestKit.
When applied to a project, it automatically:

* adds the `gradleTestKit()` dependency to the appropriate test configuration, and
* generates the plugin-under-test classpath and injects it into any `GradleRunner` instance created by your tests via link:{javadocPath}/org/gradle/testkit/runner/GradleRunner.html#withPluginClasspath--[`GradleRunner.withPluginClasspath()`].

This allows functional tests to execute a “real” Gradle build that can apply and exercise your plugin without requiring any manual classpath wiring.

NOTE: Automatic classpath injection only works when the plugin-under-test is applied in the test build using the <<plugins_intermediate.adoc#sec:plugins_block,`plugins {}` DSL>>.

By default, the Java Gradle Plugin Development plugin uses the following conventions:

* Code under test is taken from: `sourceSets.main`
* The generated plugin classpath metadata is produced from: `sourceSets.test`

These conventions can be customized using the link:{javadocPath}/org/gradle/plugin/devel/GradlePluginDevelopmentExtension.html[`GradlePluginDevelopmentExtension`].

The following sample shows the default setup for automatic plugin classpath injection:

====
include::sample[dir="snippets/reference/plugin-development/automaticClasspathInjectionQuickstart/kotlin",files="build.gradle.kts[tags=automatic-classpath]"]
include::sample[dir="snippets/reference/plugin-development/automaticClasspathInjectionQuickstart/groovy",files="build.gradle[tags=automatic-classpath]"]
====

[WARNING]
====
The automatic classpath injection provided by `GradleRunner.withPluginClasspath()` is **incompatible** with plugins that use `compileOnly` to depend on another plugin's API.

* **Symptom:** Your tests will fail with a `ClassNotFoundException` because the required base plugin classes are not included in the isolated test classpath.
* **Reason:** The recommended practice of using `compileOnly` prevents plugin API classes from being packaged with your plugin, but `withPluginClasspath` fails to correctly resolve those missing classes from the build environment.

If your plugin uses `compileOnly`, you must use a testing setup that involves:

1.  Publishing your plugin to a local Maven repository.
2.  Configuring the test project's `settings.gradle` file to pull your plugin from that local repository.
====

The following example automatically injects the code under test classes into test builds:

[source, groovy]
.src/test/groovy/org/gradle/sample/BuildLogicFunctionalTest.groovy
----
include::{snippetsPath}/reference/plugin-development/automaticClasspathInjectionQuickstart/common/src/test/groovy/org/gradle/sample/BuildLogicFunctionalTest.groovy[tag=functional-test-classpath-setup-automatic]
----

If your project uses a custom test source set (for example, a dedicated functional test suite), you can reconfigure the plugin development extension to generate the plugin classpath metadata from that source set instead.

NOTE: A dedicated DSL for modeling such test suites is provided by the incubating <<jvm_test_suite_plugin.adoc#jvm_test_suite_plugin,JVM Test Suite plugin>>.

====
include::sample[dir="snippets/reference/plugin-development/automaticClasspathInjectionCustomTestSourceSet/kotlin",files="build.gradle.kts[tags=custom-test-source-set]"]
include::sample[dir="snippets/reference/plugin-development/automaticClasspathInjectionCustomTestSourceSet/groovy",files="build.gradle[tags=custom-test-source-set]"]
====

[[sec:controlling_the_build_environment]]
== Controlling the build environment

`GradleRunner` executes test builds in an isolated environment.
Each build runs in its own dedicated working directory inside the JVM’s temporary directory (the location defined by the `java.io.tmpdir` system property, typically `/tmp`).

Because the test build runs in this isolated directory:

* Configuration from the default Gradle User Home (for example, `~/.gradle/gradle.properties`) is **not** used.
* The test build does not inherit settings, caches, or environment customizations from the machine running the tests.

The TestKit does not currently expose fine-grained control over all environmental aspects—for example, selecting a JDK for the executed build. Future versions of TestKit may offer more explicit configuration options.

TestKit uses dedicated Gradle daemon processes for the builds it runs.
These daemons are distinct from any daemons used by "normal" Gradle invocations and are automatically shut down after the tests complete.

By default, the working directories created for each test build are **not** deleted.
To keep the filesystem clean or to store TestKit state in a location managed by your build (such as a project’s `build/` directory), you can specify a custom TestKit directory using one of the following:

* The `org.gradle.testkit.dir` system property
* link:{javadocPath}/org/gradle/testkit/runner/GradleRunner.html#withTestKitDir-java.io.File-[`GradleRunner.withTestKitDir(File testKitDir)`]

[[sub:gradle-runner-gradle-version]]
== Setting the Gradle version used to test

The Gradle runner requires a Gradle distribution in order to execute the build.
The TestKit does not depend on all of Gradle's implementation.

By default, the runner will attempt to find a Gradle distribution based on where the `GradleRunner` class was loaded from.
That is, it is expected that the class was loaded from a Gradle distribution, as is the case when using the `gradleTestKit()` dependency declaration.

When using the runner as part of tests _being executed by Gradle_ (e.g. executing the `test` task of a plugin project), the same distribution used to execute the tests will be used by the runner.
When using the runner as part of tests _being executed by an IDE_, the same Gradle distribution that was used when importing the project will be used.
This means that the plugin will be effectively tested with the same version of Gradle that it is being built with.

Alternatively, a different and specific version of Gradle to use can be specified by the following `GradleRunner` methods:

* link:{javadocPath}/org/gradle/testkit/runner/GradleRunner.html#withGradleVersion-java.lang.String-[`GradleRunner.withGradleVersion(java.lang.String)`]
* link:{javadocPath}/org/gradle/testkit/runner/GradleRunner.html#withGradleInstallation-java.io.File-[`GradleRunner.withGradleInstallation(java.io.File)`]
* link:{javadocPath}/org/gradle/testkit/runner/GradleRunner.html#withGradleDistribution-java.net.URI-[`GradleRunner.withGradleDistribution(java.net.URI)`]

This can potentially be used to test build logic across Gradle versions.
The following demonstrates a cross-version compatibility test written as a Groovy Spock test:

[source, groovy]
.BuildLogicFunctionalTest.groovy
----
include::{snippetsPath}/reference/plugin-development/gradleVersion/groovy/src/test/groovy/org/gradle/sample/BuildLogicFunctionalTest.groovy[tag=functional-test-spock-gradle-version]
----

[[sub:test-kit-debug]]
== Debugging build logic

The runner uses the <<tooling_api.adoc#embedding,Tooling API>> to execute builds.
An implication of this is that the builds are executed in a separate process (i.e., not the same process executing the tests).
Therefore, executing your _tests_ in debug mode does not allow you to debug your build logic as you may expect.
Any breakpoints set in your IDE will be not be tripped by the code being exercised by the test build.

The TestKit provides two different ways to enable the debug mode:

* Setting "`org.gradle.testkit.debug`" system property to `true` for the JVM _using_ the `GradleRunner` (i.e., not the build being executed with the runner);
* Calling the link:{javadocPath}/org/gradle/testkit/runner/GradleRunner.html#withDebug-boolean-[`GradleRunner.withDebug(boolean)`] method.

The system property approach can be used when it is desirable to enable debugging support without making an ad hoc change to the runner configuration.
Most IDEs offer the capability to set JVM system properties for test execution, and this feature can be used to set the desired system property.

[[sub:test-kit-build-cache]]
== Testing with the Build Cache

To enable the <<build_cache.adoc#build_cache,Build Cache>> in your tests, you can pass the `--build-cache` argument to link:{javadocPath}/org/gradle/testkit/runner/GradleRunner.html[`GradleRunner`] or use one of the other methods described in <<build_cache.adoc#sec:build_cache_enable,Enable the Build Cache>>.
You can then check for the task outcome link:{javadocPath}/org/gradle/testkit/runner/TaskOutcome.html#FROM_CACHE[`TaskOutcome.FROM_CACHE`] when your plugin's custom task is cached.

[source, groovy]
.BuildLogicFunctionalTest.groovy
----
include::{snippetsPath}/reference/plugin-development/testKitFunctionalTestSpockBuildCache/groovy/src/test/groovy/org/gradle/sample/BuildLogicFunctionalTest.groovy[tag=functional-test-build-cache]
----

Note that TestKit re-uses a Gradle User Home between tests (see link:{javadocPath}/org/gradle/testkit/runner/GradleRunner.html#withTestKitDir-java.io.File-[`GradleRunner.withTestKitDir(java.io.File)`]), which contains the default location for the local Build Cache.
For testing with the build cache, the Build Cache directory should be cleaned between tests.
The easiest way to accomplish this is to configure the local Build Cache to use a temporary directory:

[source,groovy]
.BuildLogicFunctionalTest.groovy
----
include::{snippetsPath}/reference/plugin-development/testKitFunctionalTestSpockBuildCache/groovy/src/test/groovy/org/gradle/sample/BuildLogicFunctionalTest.groovy[tag=clean-build-cache]
----
