Modules
Intermediate⏱ 7 min read

Integration Testing

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Integration testing verifies that separate modules or services work correctly when combined. It focuses on the interfaces and data flow between units — catching issues that unit tests, which test in isolation, cannot find.

◈Key Points

  • Approaches: Big Bang (all at once), Top-Down, Bottom-Up, and Sandwich/Hybrid.
  • Common integration failures: wrong API contract, data format mismatch, authentication handshake errors.
  • Use real (or realistic) databases and services where possible — in-memory stubs hide real issues.
  • Integration tests are slower than unit tests but faster than E2E — they live in the middle of the pyramid.
  • In microservice architectures, contract testing (Pact) is a powerful form of integration testing.
⚡ Expert Pro Tip

Define and publish API contracts between teams before integration testing begins. Contract-first development eliminates the most expensive integration failures.