testing-typescript
TypeScript testing with Vitest/Jest: file structure, mocking strategy, async patterns, and coverage targets
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60%
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tessl review fix ./skills/testing-typescript/SKILL.mdTesting — 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/orsrc/__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
- Created
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