You can delete them but the fact that they are irrelevant now even though you didn't change the behaviour of the software means that it was a waste of time writ

You can delete them but the fact that they are irrelevant now even though you didn't change the behaviour of the software means that it was a waste of time writing them in the first place. Secondly it decreases your confidence in the refactor. In a classic refactor, nothing should break. This is because a good set of tests are a way of documenting and verifying the design/behaviour of the system. Finally, often in a codebase with micro tests, there will be an expectation that you replace one set of micro tests with another.