They're also dependent on what it is that you're building. If you're writing an application, the value of unit tests is limited because the APIs internal to th

They're also dependent on what it is that you're building. If you're writing an application, the value of unit tests is limited because the APIs internal to the application aren't being consumed by another developer but instead a user who's going to click/tap through an interface. So, in that case, it makes more sense to test the behavior expected to result from user interaction rather than test the return values of a given function, for instance, because it doesn't matter if a function does the right thing when the app is rendering a blank screen. You can test way more functionality at once by testing at the integration level or by writing "application" tests. Unit tests are best suited for two situations; either you've got a function where it's simply faster/easier to make sure it does the right thing by using a unit test, or you're writing an API that other developers will be consuming in their own applications.