Paste a function or class and get a set of unit tests that check behavior rather than repeat the code. It lists what the code is supposed to do, builds a test matrix (normal inputs, boundaries, bad input, errors, state and ordering), writes the tests in your framework (pytest, Jest, JUnit, Go and others), shows what to mock and what not to, and explains which bug each test would catch. It also points out code that is hard to test and suggests the smallest change that would make it testable.