How to write test cases of a software?

Now the code can be cleaned up as necessary. By re-running the test cases the developer can be confident that refactoring is not damaging any existing functionality. The concept of removing duplication is an important aspect of any software design. In this case, however, it also applies to removing any duplication between the test code and the production code—for example magic numbers or strings that were repeated in both, in order to make the test pass in step 3.