macalbert/envilder/typescript-test-doubles

Claude Code and agent skill by macalbert/envilder

Trust tier 2
  • community
LLM review pending
Source check pending

Checking that the SKILL.md file is still in the repository.

Test doubles with Vitest (vi.fn, vi.mock, vi.spyOn) and Mother pattern. Use when creating test data, mocking dependencies, or setting up module mocks in TypeScript tests.

Install

npx vskill@latest install macalbert/envilder/typescript-test-doubles

SKILL.md

Test Doubles (TypeScript)

This skill defines how to use test doubles in TypeScript (Vitest).

Test Doubles Types

1. Mock: vi.fn()

Use vi.fn() to create mock functions for port interfaces.

Purpose: Replace real dependencies with controllable test doubles.

typescript
const mockProvider: ISecretProvider = {
  getSecret: vi.fn(),
};
const mockStore: IVariableStore = {
  getMapping: vi.fn(),
  saveEnvironment: vi.fn(),
};
const mockLogger: ILogger = {
  info: vi.fn(),
  warn: vi.fn(),
  error: vi.fn(),
};
2. Stub: mockResolvedValue / mockReturnValue

Use return value methods to configure stubs.

Purpose: Predefined responses without caring about call verification.

typescript
// Async stub
mockProvider.getSecret.mockResolvedValue('secret-value');
mockStore.getMapping.mockResolvedValue({ KEY: '/ssm/path' });
// Sync stub
mockParser.parse.mockReturnValue({ config: {}, mappings: {} });
// Sequential returns
mockProvider.getSecret
  .mockResolvedValueOnce('first')
  .mockResolvedValueOnce('second');
3. Spy: vi.spyOn()

Use vi.spyOn() to observe calls on real objects without replacing behavior.

Purpose: Verify interactions while preserving real implementation.

typescript
const spy = vi.spyOn(console, 'log');
sut.execute();
expect(spy).toHaveBeenCalledWith('Processing...');
spy.mockRestore();
4. Module Mock: vi.mock()

Use vi.mock() to replace entire modules.

Purpose: Replace external dependencies (AWS SDK, file system, etc.).

typescript
vi.mock('@aws-sdk/client-ssm', () => ({
  SSMClient: vi.fn().mockImplementation(() => ({
    send: vi.fn(),
  })),
  GetParameterCommand: vi.fn(),
}));
5. Error Simulation: mockRejectedValue

Use mockRejectedValue() to simulate failures.

Purpose: Test error paths and exception handling.

typescript
mockProvider.getSecret.mockRejectedValue(
  new ParameterNotFoundError('/missing/key'),
);
mockStore.getMapping.mockRejectedValue(
  new Error('File not found'),
);

Verification Patterns

Basic Verification
typescript
expect(mockProvider.getSecret).toHaveBeenCalledWith('/ssm/path');
expect(mockProvider.getSecret).toHaveBeenCalledTimes(1);
expect(mockLogger.info).toHaveBeenCalledWith(
  expect.stringContaining('success'),
);
Not Called
typescript
expect(mockStore.saveEnvironment).not.toHaveBeenCalled();
expect(mockLogger.error).not.toHaveBeenCalled();
Call Order
typescript
expect(mockProvider.getSecret).toHaveBeenCalledBefore(
  mockStore.saveEnvironment,
);
Argument Matchers
typescript
expect(mockLogger.info).toHaveBeenCalledWith(
  expect.stringMatching(/loaded \d+ secrets/),
);
expect(mockStore.saveEnvironment).toHaveBeenCalledWith(
  expect.objectContaining({ KEY: 'value' }),
);

Mother Pattern

Use factory functions for reusable test data creation.

typescript
function createParsedMapFile(
  overrides: Partial<ParsedMapFile> = {},
): ParsedMapFile {
  return {
    config: { provider: 'aws' },
    mappings: new Map([['DB_URL', '/app/db']]),
    ...overrides,
  };
}
function createEnvilderOptions(
  overrides: Partial<EnvilderOptions> = {},
): EnvilderOptions {
  return {
    provider: SecretProviderType.AWS,
    profile: undefined,
    vaultUrl: undefined,
    ...overrides,
  };
}

Usage:

typescript
// Arrange
const mapFile = createParsedMapFile({
  mappings: new Map([['API_KEY', '/prod/api-key']]),
});

Port Test Double Pattern

Build complete mock objects implementing domain interfaces:

typescript
function createMockSecretProvider(): ISecretProvider & {
  getSecrets: Mock;
} {
  return {
    getSecrets: vi.fn().mockResolvedValue(new Map()),
  };
}
function createMockLogger(): ILogger & {
  info: Mock;
  warn: Mock;
  error: Mock;
} {
  return {
    info: vi.fn(),
    warn: vi.fn(),
    error: vi.fn(),
  };
}

Summary

Double TypeVitest APIPurpose
Mockvi.fn()Controllable replacement
Stub.mockResolvedValue() / .mockReturnValue()Predefined responses
Spyvi.spyOn()Observe real objects
Module mockvi.mock()Replace entire modules
Error sim.mockRejectedValue()Failure paths

When writing tests:

  1. Create port test doubles with vi.fn() in beforeEach
  2. Configure stubs with .mockResolvedValue() in Arrange
  3. Always verify mock interactions in Assert
  4. Use Mother pattern for complex test data
  5. Prefer vi.fn() over vi.mock() (port-level > module-level)

Security

  • Security scanPassed, 100 of 100Pattern checks on the skill's files.
  • Model reviewNot runA model review is scheduled for the next rescan.

See the full security report

Quality evaluation

  • Task evaluationNot runNo evaluation yet. Run one in Skill Studio.

See evaluation results

Source

Popularity

Repository stars
136
Repository forks
4
7-day trend score
25

Stars and forks are for the whole GitHub repository, not this skill alone. Refreshed 26 Jun 2026, 4 months ago.

Works with

Any agent vskill installs to: 56 targets in all. These 39 have a page on this site.

  • Claude Code
  • Cursor
  • GitHub Copilot
  • Windsurf
  • Codex
  • Gemini CLI
  • Cline
  • Amp
  • Roo Code
  • Goose
  • Continue
  • Kilo Code
  • Junie
  • Trae
  • OpenHands
  • Qwen Code
  • AI Agent
  • Tabnine Chat
  • Sourcegraph Cody
  • Amazon Q
  • Firebase Genkit
  • Sweep
  • Devin
  • Phind
  • Mentat
  • Claude Desktop
  • Aider
  • GPT Pilot
  • Plandex
  • bolt.new
  • v0
  • Replit Agent
  • Anse
  • TypingMind
  • BetterChatGPT
  • LibreChat
  • Warp AI
  • Pieces
  • Fig AI
Embed badge
vskill VERIFIED badge
[![vskill VERIFIED](https://verified-skill.com/api/v1/skills/macalbert/envilder/typescript-test-doubles/badge)](https://verified-skill.com/skills/macalbert/envilder/typescript-test-doubles)

Something wrong with this skill or its page? Tell us.