Writing Tests

Guidelines for writing tests in IntelliJ IDEA codebase.

For examples, see community/platform/testFramework/junit5/test/showcase/.

Prefer JUnit 5 over JUnit 4

Use JUnit 5 with @TestApplication annotation instead of extending LightJavaCodeInsightFixtureTestCase.

Why JUnit 5:

Faster: No class hierarchy overhead, shared fixtures via companion objects
Cleaner: Annotations (@TestDisposable, @RegistryKey) instead of manual setup/teardown
Flexible: Mix EDT and non-EDT tests in one class, parameterized tests, nested tests
Better isolation: Each test gets fresh disposables automatically

Shared Fixtures Pattern

Use companion object fixtures shared between all tests:

@TestApplication
internal class MyTest {
  companion object {
    private val projectFixture = projectFixture()
    private val moduleFixture = projectFixture.moduleFixture("src")
  }

  private val project get() = projectFixture.get()
  private val module get() = moduleFixture.get()
}

Lifecycle Hooks

Use JUnit 5 lifecycle annotations for setup and teardown:

@TestApplication
internal class MyTest {
  companion object {
    @JvmStatic
    @BeforeAll
    fun setUpClass() {
      // Once before all tests in class
    }

    @JvmStatic
    @AfterAll
    fun tearDownClass() {
      // Once after all tests in class
    }
  }

  @BeforeEach
  fun setUp() {
    // Before each test method
  }

  @AfterEach
  fun tearDown() {
    // After each test method
  }
}

Note: Prefer @TestDisposable over manual @AfterEach cleanup for resources.

Test Disposables

Use @TestDisposable annotation to inject test-scoped disposables (created before each test, disposed after):

@TestDisposable
lateinit var disposable: Disposable

// Or as parameter
@Test
fun myTest(@TestDisposable disposable: Disposable) { ... }

Registry Values in Tests

Use @RegistryKey annotation instead of Registry.get().setValue():

@Test
@RegistryKey(key = "my.registry.key", value = "true")
fun testWithRegistryEnabled() { ... }

System Properties in Tests

Use @SystemProperty annotation instead of System.setProperty():

@Test
@SystemProperty(propertyKey = "my.property", propertyValue = "value")
fun testWithSystemProperty() { ... }

Running Tests in EDT

Use @RunInEdt annotation to run test methods in EDT:

@TestApplication
@RunInEdt
class MyEdtTest {
  @Test
  fun testInEdt() { ... }
}

// Or for specific methods only
@TestApplication
@RunInEdt(allMethods = false)
class MyTest {
  @Test
  @RunMethodInEdt
  fun testInEdt() { ... }
}

Key Classes

com.intellij.testFramework.junit5.TestApplication - initializes shared application
com.intellij.testFramework.junit5.TestDisposable - injects test disposables
com.intellij.testFramework.junit5.RegistryKey - sets registry values
com.intellij.testFramework.junit5.SystemProperty - sets system properties
com.intellij.testFramework.junit5.RunInEdt - runs tests in EDT
com.intellij.testFramework.junit5.fixture.projectFixture - creates project fixtures
com.intellij.testFramework.junit5.fixture.moduleFixture - creates module fixtures

Showcase Tests

JUnit5ProjectFixtureTest.kt - project fixture patterns
JUnit5DisposableTest.kt - disposable injection
JUnit5SystemPropertyTest.kt - system property usage
JUnit5RunInEdtTest.java - EDT execution

Running Tests

To run tests via command line, see TESTING.md.

Quick example:

./tests.cmd -Dintellij.build.test.patterns=*MyTest

writing-tests