Testing Strategies and Methodologies

Testing Pyramid

         /  E2E   \          ~5-10% of tests
        / --------- \
       / Integration  \      ~15-25% of tests
      / --------------- \
     /    Unit Tests      \   ~65-80% of tests
    /______________________\

Unit tests form the base. Fast (milliseconds), test a single function or class in isolation. When one fails, it should point to exactly what broke.

Integration tests verify components work together: a service calling a database, two modules interacting, an HTTP handler processing a request through the application. Slower, more setup, but catch issues unit tests cannot.

End-to-end tests simulate real user behavior through the full stack. Slow, expensive to maintain, prone to flakiness. Use sparingly for critical user journeys only.