unit-testing
2 free lessons tagged unit-testing across Programming. Each one is a short sequence of focused steps with narration and a five-question quiz at the end — take them in any order, no signup required.
Test Doubles: Isolation and What It Costs
Replacing a real dependency with a stand-in is what makes a unit test fast, deterministic, and able to reach states you cannot otherwise produce. It is also how a suite ends up green while the system is broken. This lesson covers the five kinds of double, when each is right, and the two failure modes that follow every team who reaches for mocks by reflex.
What Is Worth Testing, and the Shape That Follows
Every test costs time to write, time to run, and time to maintain when the code moves. This lesson works out what that budget should buy: what each level of test can and cannot catch, why the pyramid has the shape it does, why some teams invert it, and the arithmetic that decides both questions before anyone argues about it.