In a next step, we will remove tests from each file to have a per-binary
split of tests. This will help identify which tests fail most often on
Travis CI.
In another future step, we will split the large one_test into several
auto tests, which will make testing quite a bit slower (adding about 10
seconds setup time to each), but hopefully a lot more stable ("Tox went
offline" should not happen as much anymore).
