MEPX
Chapter 2 of 10All chapters
  1. 1Why test
  2. 2Kinds of test
  3. 3What a good test looks like
  4. 4Fakes, stubs and mocks
  5. 5Coverage and flakiness
  6. 6Reproducing a bug
  7. 7Narrowing it down
  8. 8Reading the evidence
  9. 9Debuggers and tools
  10. 10The hard ones

Chapter 2 of 10

Kinds of test

The pyramid, and why it is that shape.

Three levels

Unit tests check one piece in isolation and run in milliseconds. Integration tests check that pieces work together, including real databases. End to end tests drive the whole system as a user.

  • Many unit, some integration, few end to end: fast feedback where it is cheapest.
  • End to end tests find the most realistic bugs and are the slowest and most brittle.

Other useful kinds

Property based tests generate many inputs and check a rule holds. Snapshot tests catch unintended output changes. Contract tests keep two services agreeing about their interface.