intellij-sdk-code-samples/topics/basics/testing_plugins/light_and_heavy_tests.md

Light and Heavy Tests

Introduction to light tests reusing a single project for multiple tests, and heavy tests creating a new project for each test.

Plugin tests run in a real, rather than mocked, IntelliJ Platform environment and use real implementations for most application and project services.

Loading and initializing all the project components and services for a project to run tests is a relatively expensive operation, and it is desired to avoid doing it for each test. Dependently on the loading and execution time, we make a difference between light tests and heavy tests available in the IntelliJ Platform test framework:

• Light tests reuse a project from the previous test run when possible.
• Heavy tests create a new project for each test.

Light and heavy tests use different base classes or fixture classes, as described below.

Because of the performance difference, we recommend plugin developers to write light tests whenever possible.

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Light Tests

The standard way of writing a light test is to extend one of the following classes:

Use LightPlatformTestCase or BasePlatformTestCase for tests that don't have any dependency on Java functionality.

Examples:

• JavaCopyrightTest
• HtmlDocumentationTest
• AcceptWordAsCorrectTest

An explicit dependency on TestFramework.Plugin.Java is required, see test-framework dependencies.

{title="Java Test Framework (2024.2+)"}

For tests that require the Java PSI or related functionality:

• LightJavaCodeInsightFixtureTestCase for JUnit 3
• LightJavaCodeInsightFixtureTestCase4 for JUnit 4 (2021.1 and later)
• LightJavaCodeInsightFixtureTestCase5 for JUnit 5 (2021.1 and later)

Examples:

• PatternValidatorTest (JUnit 3)
• JavaCtrlMouseTest (JUnit 4)
• MissingJavadocHighlightingTest (JUnit 5)

See on how to set up your test environment to obtain the required Mock JDK automatically.

LightProjectDescriptor

When writing a light test, it is possible to specify the requirements of the project used in test, such as the module type, the configured SDK, facets, libraries, etc. It is done by extending the LightProjectDescriptor class and returning the project descriptor (usually stored in static final field) from getProjectDescriptor().

Before executing each test, the project instance will be reused if the test case returns the same project descriptor as the previous one or recreated if the descriptor is different (equals() = false).

When testing JVM languages, see also DefaultLightProjectDescriptor.

Heavy Tests

The standard way of writing a heavy test is to extend HeavyPlatformTestCase.

Examples:

• ModuleDeleteProviderTest
• FacetTypeUnloadingTest
• SourceFolderManagerTest

Setting Up a Multi-Module Project

If a test requires a multi-module project, using a heavy test is required. The following code snippet presents a multi-module Java project setup:

TestFixtureBuilder<IdeaProjectTestFixture> projectBuilder =
    IdeaTestFixtureFactory.getFixtureFactory().createFixtureBuilder(getName());

// fixture must be created before adding modules:
myFixture = JavaTestFixtureFactory.getFixtureFactory()
    .createCodeInsightFixture(projectBuilder.getFixture());

// add and configure modules:
JavaModuleFixtureBuilder<?> builder1 =
    projectBuilder.addModule(JavaModuleFixtureBuilder.class);
// optionally, configure the module, e.g.:
// builder1.setLanguageLevel(...);
// builder1.addJdk(...);

JavaModuleFixtureBuilder<?> builder2 =
    projectBuilder.addModule(JavaModuleFixtureBuilder.class);
// configure another module...