Copilot instructions

1---
2description: VS Code test writing guidelines — unit tests, integration tests, snapshot tests, and clean teardown patterns. Reference when writing or updating tests.
3applyTo: "{src/vs/**/test/**,src/vs/**/*.test.ts,src/vs/**/*.integrationTest.ts}"
4---
5 
6# Writing Tests
7 
8Canonical reference: https://github.com/microsoft/vscode/wiki/Writing-Tests
9 
10## Test Types
11 
12| Type | File suffix | Location | Runs in |
13|------|-------------|----------|---------|
14| Unit tests | `.test.ts` | `src/vs/**/test/` | Browser, Electron, or Node.js (depends on layer) |
15| Integration tests | `.integrationTest.ts` | `src/vs/**/test/` | Real external APIs |
16| Extension tests | Standard extension test system | `extensions/*/` | Extension host |
17 
18## Running Tests
19 
20- **Unit tests:** `scripts/test.sh` (macOS/Linux) or `scripts/test.bat` (Windows)
21  - Filter: `--grep <pattern>`
22  - Glob: `--runGlob **/myFile.test.js`
23- **Integration tests:** `scripts/test-integration.sh` or `scripts/test-integration.bat`
24- **VS Code UI:** Use the [Selfhost Test Provider](https://marketplace.visualstudio.com/items?itemName=ms-vscode.vscode-selfhost-test-provider)
25 
26## Writing Unit Tests
27 
28Tests use Mocha's BDD interface (`suite`/`test`) with the `assert` module and `sinon` for mocks.
29 
30### Clean Teardown
31 
32Always use `ensureNoDisposablesAreLeakedInTestSuite()` to catch disposal leaks:
33 
34```typescript
35suite('myTests', () => {
36  const store = ensureNoDisposablesAreLeakedInTestSuite();
37 
38  test('example', () => {
39    const disposable = store.add(new MyDisposable());
40    // ...
41  });
42});
43```
44 
45Always call `sinon.restore()` in `teardown` to avoid leaking mocks.
46 
47### Best Practices
48 
49- Minimize assertions per test — prefer one `assert.deepStrictEqual` snapshot over many fine-grained assertions
50- Don't add tests to the wrong suite — find the relevant `suite` block
51- Follow existing patterns (`describe`/`test` or `suite`/`test`) consistently within a file
52- Don't stub globals (e.g., `(mainWindow as any).X = ...`) — make dependencies injectable instead
53 
54### Snapshot Testing
55 
56Use `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.
57