Let AI Write Your Unit Tests: A Practical Guide
Stop spending hours writing tests. Learn how Claude Code can generate comprehensive test suites in minutes.
describe('UserService', () => {
it('should create user', ...);
it('should validate email', ...);
it('should hash password', ...);
});
The Testing Time Sink
Writing unit tests is essential but tedious. For every hour spent writing code, you might spend another hour writing tests. Edge cases, mocking dependencies, setting up fixtures - it all adds up.
Claude Code changes this equation entirely. It can analyze your code, understand the logic, and generate comprehensive tests that cover happy paths, edge cases, and error conditions - all in seconds.
Basic Test Generation
The simplest approach - just ask Claude to write tests:
# Simple prompt
"Write unit tests for the UserService class in src/services/user.ts"
Claude will analyze the class, understand its methods, and generate tests that cover the main functionality.
Advanced Test Prompts
Coverage-Focused Tests
"Write unit tests for UserService with 100% branch coverage. Include tests for:
- All happy path scenarios
- Error conditions (invalid input, network failures)
- Edge cases (empty strings, null values, boundary conditions)"
Pattern-Matching Tests
"Write tests for PaymentService following the same patterns used in src/tests/user.test.ts. Use the same mocking approach and assertion style."
Integration Test Generation
"Write integration tests for the /api/orders endpoint. Test the full request-response cycle including database operations. Use our test database configuration from jest.config.js"
What Claude Code Generates
A well-prompted request typically produces:
- Test file setup: Imports, mocks, beforeEach/afterEach hooks
- Describe blocks: Logical grouping of related tests
- Individual test cases: Clear descriptions and assertions
- Mock implementations: Proper mocking of dependencies
- Edge case coverage: Null checks, boundary conditions, error states
Real Example
Given this simple function:
// src/utils/validation.ts
export function validateEmail(email: string): boolean {
if (!email) return false;
return /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email);
}
Claude generates:
// src/utils/validation.test.ts
import { validateEmail } from './validation';
describe('validateEmail', () => {
// Happy path
it('returns true for valid email', () => {
expect(validateEmail('user@example.com')).toBe(true);
});
// Edge cases
it('returns false for empty string', () => {
expect(validateEmail('')).toBe(false);
});
it('returns false for null/undefined', () => {
expect(validateEmail(null as any)).toBe(false);
});
// Invalid formats
it('returns false for missing @', () => {
expect(validateEmail('userexample.com')).toBe(false);
});
// ... more tests
});
Best Practices
- Review generated tests: AI can miss business logic nuances
- Run them: Always verify tests actually pass (or fail when expected)
- Add domain-specific cases: You know edge cases AI might miss
- Use as a starting point: Refine and expand the generated tests
Monitor Test Runs Remotely
Generating tests is fast, but running large test suites takes time. With Bridge Terminal, you can kick off a test run and monitor the results from your phone. Get notified when tests complete or if Claude needs input on failing tests.
Monitor Your Test Suites
Run tests and get notified on results from anywhere.
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