When to use debug vs unit tests?

Question

I'am a little bit confused what is better to use debug or write unit test? and is this general or there are cases where debug better than unit test?or should I use both of them?

Thanks

Answer 1

Unit test is used to ensure that code works as expected. Debug is used when you need to find why the code doesn't work as expected.

Answer 2

Debugging will help you diagnose non-working code.

Unit tests provide the following:

1. a repeatable means of determining that your code works, both for common scenarios and for edge cases. They will allow you to refactor your code with confidence that it still works.
2. a demonstrable specification of the code. In the absence of a written specification your unit tests are your code's specification. This is particularly true in the Agile world.
3. an aid to building well-structured code. Because you want to run unit tests standalone, you have to write your classes under test to accept different (sometimes mocked) datasources, sinks etc. By encouraging these abstractions and separation of concerns, your code will become well-structured (you can, of course, write well-structured code without unit tests)

Your unit tests should be run repeatedly (most often as part of your build process). If you do break them (most often due to a programming error), then it's time to break out the debugger to identify the issues and fix up the code (or perhaps amend the test) accordingly.