run-tests: $TESTDIR can be something else than $PWD $TESTDIR is expected to be the directory were the test lives, and is often used to reference helper functions. However, it is now set to $PWD at test invocation time, so if `run-tests.py` is called from another folder, the test will fail. The solution is to force $TESTDIR to be the base directory of the test itself, irrespective of where the runner is called from.