vscode/.github/instructions/writing-tests.instructions.md

description, applyTo

description	applyTo
VS Code test writing guidelines — unit tests, integration tests, snapshot tests, and clean teardown patterns. Reference when writing or updating tests.	{src/vs/**/test/**,src/vs/**/*.test.ts,src/vs/**/*.integrationTest.ts}

Writing Tests

Canonical reference: https://github.com/microsoft/vscode/wiki/Writing-Tests

Test Types

Type	File suffix	Location	Runs in
Unit tests	.test.ts	src/vs/**/test/	Browser, Electron, or Node.js (depends on layer)
Integration tests	.integrationTest.ts	src/vs/**/test/	Real external APIs
Extension tests	Standard extension test system	extensions/*/	Extension host

Running Tests

• Unit tests: scripts/test.sh (macOS/Linux) or scripts/test.bat (Windows)
  • Filter: --grep <pattern>
  • Glob: --runGlob **/myFile.test.js
• Integration tests: scripts/test-integration.sh or scripts/test-integration.bat
• VS Code UI: Use the Selfhost Test Provider

Writing Unit Tests

Tests use Mocha's BDD interface (suite/test) with the assert module and sinon for mocks.

Clean Teardown

Always use ensureNoDisposablesAreLeakedInTestSuite() to catch disposal leaks:

suite('myTests', () => {
  const store = ensureNoDisposablesAreLeakedInTestSuite();

  test('example', () => {
    const disposable = store.add(new MyDisposable());
    // ...
  });
});

Always call sinon.restore() in teardown to avoid leaking mocks.

Best Practices

• Minimize assertions per test — prefer one assert.deepStrictEqual snapshot over many fine-grained assertions
• Don't add tests to the wrong suite — find the relevant suite block
• Follow existing patterns (describe/test or suite/test) consistently within a file
• Don't stub globals (e.g., (mainWindow as any).X = ...) — make dependencies injectable instead

Snapshot Testing

Use assertSnapshot for Jest-like snapshot tests. Snapshots are written to a __snapshots__ directory beside the test file on first run — verify the output is correct, then subsequent runs compare against it.