DorrisWord
Test
A test is a small piece of code whose only job is to check that another piece still does what it is supposed to do.
Also called: tests, test suite, green, red
It sets something up, runs the real thing, and says whether the answer was what it should have been. Your project holds a pile of them, and one command runs them all. Passing is usually called green, failing red.
You'll meet them every time you change something, which is the point: not to prove the new thing works, but to prove the old things still do. The type check runs alongside them.
The one to watch for is a test that would pass even with the feature broken. Have your agent break something on purpose and show you a test catching it.