Verifying server code.
WHAT TO TEST AT EACH LEVEL
- Unit: business rules, without infrastructure
- Integration: the application with a real database
- End to end: complete paths through the system
WHAT PROPORTION
Many unit tests, fewer integration, few end to end.
WHY
Unit tests are fast and precise; end-to-end tests are slow and fragile.
WHAT TO TEST WITH A REAL DATABASE
Anything involving queries.
WHY
Substituted databases do not reproduce real behaviour, and query faults are exactly what you need to catch.
WHAT TO SUBSTITUTE
External services, so tests do not depend on them.
WHAT TO TEST FOR EVERY ENDPOINT
The success path Invalid input Missing authentication Insufficient authorisation Not found
WHY THOSE LAST THREE
They are the paths most often broken and least often tested.
WHAT TO ENSURE
That tests are independent and can run in any order.
WHAT TO DO ABOUT TEST DATA
Create what each test needs, and clean up.
WHAT TO RUN AUTOMATICALLY
Everything, on every change.
WHAT A FLAKY TEST MEANS
Something is wrong. Investigate rather than rerunning.
