[ivanb]

In practice e2e tests don't cover all code paths and raise a question: what is the point? There is a code path explosion when going from a unit to an endpoint. A more low-level test can cover all code paths of every small unit, whereas tests at service boundary do not in practice do that. Even if they did, there would be a lot of duplication because different service endpoints would reuse the same units. Thus, I find e2e tests very limited in usability. They can demonstrate that the whole stack works together on a happy path, but that's about it.

[strogonoff]

You are testing that the software works. I think that is higher value than testing all possible code paths in isolation, and then still not having the guarantee that it all works.

[stavros]

The problem tends to be that programs most often break at the integration boundaries, though.