I think they were contrasting the first test (a more specific test of a leaf function, i.e the innermost parts of the app) with second test (a less specific te

I think they were contrasting the first test (a more specific test of a leaf function, i.e the innermost parts of the app) with second test (a less specific test because it fails when either the outermost or innermost part is broken) and saying that to diagnose the second kind of test failure, you can make note of the fact that the more specific test is failing as well and start your debugging in that innermost part of the app (the leaf of the callstack).