Reorganize test suite slightly

[SimonAlling]

Today, most test failures contain a redundant "Achtung, die Kurve!" line:

↓ AchtungTest
↓ Achtung, die Kurve!
↓ Crashing into a Kurve
✗ Hitting a Kurve's tail end is a crash

This PR makes it look like this instead:

↓ AchtungTest
↓ Crashing into a Kurve
✗ Hitting a Kurve's tail end is a crash

It also makes it easier to get an overview of the test suite by listing the four sub-suites together without any inlined test cases.

💡 git show --color-moved