$TESTDIR is added to the path, so this is superfluous. Also,
inconsistent use of quotes means we might have broken on tests with
paths containing spaces.
Many tests didn't change back from subdirectories at the end of the tests ...
and they don't have to. The missing 'cd ..' could always be added when another
test case is added to the test file.
This change do that tests (99.5%) consistently end up in $TESTDIR where they
started, thus making it simpler to extend them or move them around.