Verifying behaviour automatically.
WHAT A TEST IS
Code that checks your code does what it should.
WHY BOTHER
Changes can be made without fear Bugs are caught before deployment The test documents intended behaviour
WHAT TO TEST FIRST
The logic that matters most Anything that has broken before Edge cases and failure paths
WHAT NOT TO TEST
Trivial code Library behaviour Everything, if that prevents you testing anything
WHAT A GOOD TEST IS
Fast Independent of other tests Deterministic Clear about what it checks
WHAT MAKES TESTS PAINFUL
Dependence on external services Dependence on a database Dependence on timing
WHAT TO DO ABOUT THOSE
Separate logic from external access, so logic can be tested alone.
That single structural decision makes testing possible.
WHAT TO RUN THEM WITH
An established test framework.
WHEN TO RUN THEM
Before every deployment, at minimum.
WHAT A FAILING TEST MEANS
Either the code or the test is wrong. Establish which.
