  File "/Users/abdul/.virtualenvs/pc36/lib/python3.6/site-packages/_pytest/vendored_packages/pluggy.py", line 595, in execute
    return _wrapped_call(hook_impl.function(*args), self.execute)

  File "/Users/abdul/.virtualenvs/pc36/lib/python3.6/site-packages/_pytest/vendored_packages/pluggy.py", line 247, in _wrapped_call
    call_outcome = _CallOutcome(func)

  File "/Users/abdul/.virtualenvs/pc36/lib/python3.6/site-packages/_pytest/vendored_packages/pluggy.py", line 264, in __init__
    self.result = func()

  File "/Users/abdul/.virtualenvs/pc36/lib/python3.6/site-packages/_pytest/vendored_packages/pluggy.py", line 596, in execute
    res = hook_impl.function(*args)

  File "/Users/abdul/.virtualenvs/pc36/lib/python3.6/site-packages/_pytest/runner.py", line 90, in pytest_runtest_call
    item.runtest()

  File "/Users/abdul/Code/PieCrust2/tests/conftest.py", line 328, in runtest
    fs = self._prepareMockFs()

  File "/Users/abdul/Code/PieCrust2/tests/conftest.py", line 127, in _prepareMockFs
    fs.withConfig(config)

  File "/Users/abdul/Code/PieCrust2/tests/basefs.py", line 56, in withConfig
    yaml.dump(config))

  File "/Users/abdul/Code/PieCrust2/tests/basefs.py", line 42, in withFile
    self._createFile(path, contents)

  File "/Users/abdul/Code/PieCrust2/tests/tmpfs.py", line 67, in _createFile
    fp.write('\n'.join(traceback.format_stack(limit=10)))
