Your First Unit Test

Write and run a real unit test from scratch: learn the Arrange-Act-Assert shape, watch a test pass green and fail red, and pick up the habits that make a test worth keeping.

1. Arrange, Act, Assert Every test, in every language, has the same three parts: arrange the inputs, act by calling the code, assert the result is what you expected. We map them onto a tiny real function.
2. Write It and Run It Create the test file, run pytest, and read a green pass - then break the code on purpose to see a red failure and learn to read the expected-vs-actual output.
3. What Makes a Good Test The habits that make a test trustworthy: test one behavior, name it for what it checks, keep it fast and independent, cover the edge cases, and never trust a test that passes even when the code is wrong.