Tests should not generally need to be rewritten unless you’re changing the externally-visible behavior API of a function or library (either the literal API, its

Tests should not generally need to be rewritten unless you’re changing the externally-visible behavior API of a function or library (either the literal API, its effects, or its semantics). If you’re changing the tests because you’ve changed the internal, non-externally-visible logic of your code, your tests are almost certainly providing you negative value. Being able to refactor and re-run your existing test suite to ensure consistent behavior is possibly the important property of a good test suite.