# Part 4: Writing a Unit Test

version 9.5.0-20260319005705+0000

Learn the basics of unit testing your plugin to ensure it behaves as expected.

In this section, you’ll:

- Update the default unit test to verify your plugin’s functionality.

- Run the unit tests to confirm your plugin registers its task correctly.

## Step 0: Before you Begin

1. You initialized your plugin in part 1.

2. You added an extension to your plugin in part 2.

3. You created a custom task in part 3.

## Step 1: About Unit Tests

Gradle `init` creates a sample unit test to get you started.

It’s located in `src/test/kotlin/org/example/PluginTutorialPluginTest.kt`.

It’s located in `src/test/groovy/org/example/PluginTutorialPluginTest.groovy`.

The original test is simple, it applies the default `org.example.greeting` plugin and verifies that the `greeting` task is available. We will update it to test our new plugin.

## Step 2: Update the Test

First, let’s rename the test file to match our plugin’s name.

Rename the file `PluginTutorialPluginTest.kt` to `SlackPluginTest.kt`.

Rename the file `PluginTutorialPluginTest.groovy` to `SlackPluginTest.groovy`.

Next, update the code to reflect our plugin’s ID (`org.example.slack`) and task name (`sendTestSlackMessage`).

plugin/src/test/kotlin/org/example/SlackPluginTest.kt

    package org.example

    import org.gradle.testfixtures.ProjectBuilder
    import kotlin.test.Test
    import kotlin.test.assertNotNull

    class SlackPluginTest {
        @Test fun `plugin registers task`() {
            // Create a test project and apply the plugin
            val project = ProjectBuilder.builder().build()
            project.plugins.apply("org.example.slack")

            // Verify the result
            assertNotNull(project.tasks.findByName("sendTestSlackMessage"))
        }
    }

plugin/src/test/groovy/org/example/SlackPluginTest.groovy

    package org.example

    import org.gradle.testfixtures.ProjectBuilder
    import org.gradle.api.Project
    import spock.lang.Specification

    class SlackPluginTest extends Specification {
        def "plugin registers task"() {
            given:
            def project = ProjectBuilder.builder().build()

            when:
            project.plugins.apply("org.example.slack")

            then:
            project.tasks.findByName("sendTestSlackMessage") != null
        }
    }

This test:

1. `ProjectBuilder.builder().build()`: Creates an in-memory test project, which is perfect for isolating our plugin’s behavior.

2. `project.plugins.apply(…​)`: Applies our `SlackPlugin` to the test project.

3. `assertNotNull(…​)`: Confirms that our `sendTestSlackMessage` task was successfully registered by the plugin.

## Step 3: Run the Test

You can now run the `test` task from the command line to make sure everything is working correctly.

    $ ./gradlew test

    > Task :plugin:checkKotlinGradlePluginConfigurationErrors SKIPPED
    > Task :plugin:processTestResources NO-SOURCE
    > Task :plugin:pluginDescriptors UP-TO-DATE
    > Task :plugin:processResources UP-TO-DATE
    > Task :plugin:compileKotlin UP-TO-DATE
    > Task :plugin:compileJava NO-SOURCE
    > Task :plugin:classes UP-TO-DATE
    > Task :plugin:pluginUnderTestMetadata UP-TO-DATE
    > Task :plugin:jar UP-TO-DATE
    > Task :plugin:compileTestKotlin
    > Task :plugin:compileTestJava NO-SOURCE
    > Task :plugin:testClasses UP-TO-DATE
    > Task :plugin:test

    BUILD SUCCESSFUL in 1s
    7 actionable tasks: 2 executed, 5 up-to-date

If your test passes, you’ve successfully verified that your plugin is registering its custom task as intended!

Next Step: Add a DataFlow Action >>