good idea where it might end up running inside of libsystemd.so or
similar. Hence, use TLS (i.e. `thread_local`) where appropriate, and maybe
the occasional `pthread_once()`.
+
+## Tests
+
+- Use the assertion macros from `tests.h` (`ASSERT_GE()`, `ASSERT_OK()`, ...) to
+ make sure a descriptive error is logged when an assertion fails. If no assertion
+ macro exists for your specific use case, please add a new assertion macro in a
+ separate commit.
+
+- When modifying existing tests, please convert the test to use the new assertion
+ macros from `tests.h` if it is not already using those.