Adding Tests to Your Codex CLI Project

Most Codex CLI projects ship with zero tests. This means every change is a gamble — you might fix one thing and break three others without knowing until a user reports it. Tests are automated checks that verify your app works correctly. They run in seconds and catch bugs before your users do.

Codex can generate tests if you ask it to, but they're often shallow. Set up pytest for Python or Vitest for TypeScript. Write tests against the generated functions directly, using parameterize decorators to cover edge cases the generated code might miss

Focus tests on input boundary conditions — empty inputs, null values, very large inputs, and malformed data. Test error paths explicitly since Codex rarely handles them. For any API code, test authentication, authorization, and input validation separately from business logic

Unit tests check individual functions in isolation — does this function calculate the right total? Integration tests check that multiple pieces work together — does submitting this form save to the database? End-to-end (E2E) tests simulate a real user — can someone sign up, log in, and complete a purchase? Start with E2E tests for your most critical flows, then add integration tests for your API endpoints.

Set up your tests to run automatically on every code push using GitHub Actions or a similar CI service. This way, you'll know immediately if a change breaks something. A basic CI pipeline runs your tests, checks for TypeScript errors, and builds the project. If any step fails, the push is flagged before it reaches production.