They are valuable in different ways. Integration tests are better at accurately reflecting the real software. There is less of a leap of faith between "this te

They are valuable in different ways. Integration tests are better at accurately reflecting the real software. There is less of a leap of faith between "this test passes" and "the software actually works". Unit tests are better at telling you exactly what failed. There is less of a research project between "this test fails" and "this code right here needs to be fixed". I don't really love anxiety-inducing leaps of faith or time-consuming research projects, but I don't know of one form of testing that avoids both.