Avoid `expectFail` in the test suite

[fendor]

expectFail interprets a test failure for any reason as a success. But since we don't check why exactly the test is failing, we lose valuable information. Thus, many of the tests that use expectFail are likely not really testing what they are supposed to be.

In my opinion, we should replace all occurrences of expectFail with an assertion that shows what is failing precisely, or delete/ignore the respective test case.