The units we test are almost never big enough for internal refactoring. It’s the decomposition into units that wants refactoring, and there the test suite activ

The units we test are almost never big enough for internal refactoring. It’s the decomposition into units that wants refactoring, and there the test suite actively fights back (mock expectations in particular). If there were enough code involved in a test that we could meaningfully refactor it while keeping the test green, we would call it an integration test.