What is vscode writing-tests.instructions.md?

Test-writing guidelines for VS Code, covering unit tests, integration tests, extension tests, and snapshot tests. They also explain TDD-style test structure and cleanup practices.

Adding or updating tests with Mocha, assert, and Sinon; choosing the right test type; filtering test runs; and ensuring test resources are cleaned up.

They make it clearer where tests belong, how to run them, and how to avoid leaked resources or leftover mocks that can make later tests unreliable.

vscode writing-tests.instructions.md — Instructions file by microsoft

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods

npx agentmods add instructions/microsoft/vscode/writing-tests

Clone the repo

git clone --depth 1 https://github.com/microsoft/vscode

Made for: GitHub Copilot.

Per session 558 This file is loaded in full into every session.

When invoked 558 The same file — it is already loaded in full.

Security scan A 0 findings. Scan, not verified.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5	$0.00558	$0.00558
Opus 5	$0.00279	$0.00279
Sonnet 5	$0.00112	$0.00112
Haiku 4.5	$0.00056	$0.00056

Measured yesterday against content hash 7e5748d8fe12, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

vscode writing-tests.instructions.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.github/instructions/writing-tests.instructions.md · 57 lines

How it starts

The opening of the file, as written. The whole thing — 57 lines — stays where its author put it; the contents beside it link to each section on GitHub.

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.

Read the full file on GitHub · 57 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

yesterday First seen · 57 lines · 558 tokens per session scan A 7e5748d8fe12

Subscribe to this mod's changes

vscode writing-tests.instructions.md is an instructions file published in the GitHub repository microsoft/vscode (190,061 stars, last pushed yesterday), licensed MIT. It adds 558 tokens to every session, about $0.0028 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Languages Testing Writing and docs editor electron microsoft typescript visual-studio-code

vscode writing-tests.instructions.md

Getting it into your agent

What it costs to keep this loaded

Grade A, and why

Nothing flagged

How it starts

Writing Tests

Test Types

Running Tests

Writing Unit Tests

Clean Teardown

Best Practices

Snapshot Testing

What this file has done since we first saw it

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