The other point about unit tests is that they allow you to test far more permutations. At a micro level, you can test more of the possible types of inputs to yo

The other point about unit tests is that they allow you to test far more permutations. At a micro level, you can test more of the possible types of inputs to your function. When you move to integration tests, the permutations multiply to the point that it would require billions of tests to test the same range of inputs. This is why both are so necessary. Integration testing tests whether the whole thing is coherent when put together. But it’s terrible for testing edge cases and error scenarios. That’s where unit testing comes in. It gives the developer a chance to codify every edge case they’ve considered to automate the process of catching regressions.