unit-tests

name	unit-tests
description	Unit test writing with Jest (JS/TS) or pytest (Python). Test structure, mocking, edge cases, coverage. Don't use for E2E or integration tests.
model	sonnet
effort	medium
allowed-tools	Read, Write, Edit, Bash, Grep
paths	**/*.test.ts,**/*.test.tsx,**/*.spec.ts,**/test_*.py,**/*_test.py

Unit Testing

Structure (Arrange-Act-Assert)

describe('ServiceName', () => {
  it('should [expected behavior] when [condition]', () => {
    // Arrange: setup
    // Act: call function
    // Assert: verify result
  });
});

What to Test

• Happy path (normal operation)
• Edge cases (empty, null, boundary values)
• Error cases (invalid input, network failure)
• Business logic (calculations, transformations)

Mocking

• Mock external dependencies (DB, API, filesystem)
• Never mock the thing you're testing
• Use dependency injection for testability

Coverage Target

• New code: 80%+ line coverage
• Critical paths: 100%