We should not rely on **/*.spec.js globs in karma config. It is bad.
Why is it bad ?
Because depending on your environment, the order of tests might change. Running tests randomly is a good thing when you know it's going to be random. Here, we don't really know it and so one day tests will break and we'll spend an afternoon wondering why the ordering of the tests changed and why it broke our tests.
Having an "app.spec.js" file importing every other spec file sure is annoying to maintain, but at least it lets us control the order of the tests. It also lets us apply "global" mocks once for all tests, for example mocking TLP.
Finally, it means webpack compiles only one bundle of files for tests.