> If none of your tests fail then does it really matter?
Yes. Absolutely.
You don't believe your software is correct because your tests don't fail. You believe your software is correct because you have a mental model of your code. If your tests are not failing but your software is not behaving correctly, that your mental model of your code is broken.
Yes. Absolutely.
You don't believe your software is correct because your tests don't fail. You believe your software is correct because you have a mental model of your code. If your tests are not failing but your software is not behaving correctly, that your mental model of your code is broken.