This is important when used with ``pytester``'s ``runpytest_inprocess``.
Since 07f20ccab `pytest testing/acceptance_test.py -k test_doctest_id`
would fail, since the second run would not consider the exception to be
an instance of `doctest.DocTestFailure` anymore, since the module was
re-imported, and use another failure message then in the short test
summary info (and in the report itself):
> FAILED test_doctest_id.txt::test_doctest_id.txt - doctest.DocTestFailure: <Do...
while it should be:
> FAILED test_doctest_id.txt::test_doctest_id.txt
Daniel Hahler