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testing-typescript

TypeScript testing with Vitest/Jest: file structure, mocking strategy, async patterns, and coverage targets

54

Quality

60%

Does it follow best practices?

Impact

—

No eval scenarios have been run

SecuritybySnyk

Passed

No known issues

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SKILL.md
Quality
Evals
Security

Testing — TypeScript

Framework

  • Vitest for new projects (fast, native ESM, Jest-compatible API).
  • Jest only if already configured — don't mix frameworks.
  • Run: vitest run / vitest run --coverage

File Conventions

  • Co-locate: src/utils/format.ts → src/utils/format.test.ts
  • Shared fixtures: tests/fixtures/ or src/__tests__/helpers/

Test Structure

describe('formatDate', () => {
  it('should return ISO date string when given a valid Date', () => {
    // Arrange
    const date = new Date('2026-01-15');

    // Act
    const result = formatDate(date);

    // Assert
    expect(result).toBe('2026-01-15');
  });
});

Mocking

// Module mock — top of file
vi.mock('../services/emailService');

// Spy without full mock
const spy = vi.spyOn(mailer, 'send').mockResolvedValue(undefined);

// Restore after each test
afterEach(() => vi.restoreAllMocks());

// Time control
beforeEach(() => vi.useFakeTimers());
afterEach(() => vi.useRealTimers());

Async Tests

// Always await; use assertions count for safety
it('should reject with AuthError when token is expired', async () => {
  expect.assertions(1);
  await expect(verifyToken('expired')).rejects.toThrow('Token expired');
});

Coverage Targets

  • Business logic: 85%+ branch coverage.
  • Utility functions: 100% line coverage.
  • Do not write tests just to hit numbers — test behavior.
Repository
ucdavis/ai-skills-registry
Commit

c0b2e4b

Last updated
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