`pytest -m a/`

output.txt

=============================================================== test session starts ===============================================================
platform linux -- Python 3.7.0, pytest-3.8.1, py-1.6.0, pluggy-0.7.1
rootdir: /tmp/pytest_repro, inifile:
collecting 1 item                                                                                                                                 INTERNALERROR> Traceback (most recent call last):
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/_pytest/main.py", line 178, in wrap_session
INTERNALERROR>     session.exitstatus = doit(config, session) or 0
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/_pytest/main.py", line 214, in _main
INTERNALERROR>     config.hook.pytest_collection(session=session)
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/pluggy/hooks.py", line 258, in __call__
INTERNALERROR>     return self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/pluggy/manager.py", line 67, in _hookexec
INTERNALERROR>     return self._inner_hookexec(hook, methods, kwargs)
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/pluggy/manager.py", line 61, in <lambda>
INTERNALERROR>     firstresult=hook.spec_opts.get('firstresult'),
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/pluggy/callers.py", line 201, in _multicall
INTERNALERROR>     return outcome.get_result()
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/pluggy/callers.py", line 76, in get_result
INTERNALERROR>     raise ex[1].with_traceback(ex[2])
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/pluggy/callers.py", line 180, in _multicall
INTERNALERROR>     res = hook_impl.function(*args)
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/_pytest/main.py", line 224, in pytest_collection
INTERNALERROR>     return session.perform_collect()
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/_pytest/main.py", line 432, in perform_collect
INTERNALERROR>     session=self, config=self.config, items=items
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/pluggy/hooks.py", line 258, in __call__
INTERNALERROR>     return self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/pluggy/manager.py", line 67, in _hookexec
INTERNALERROR>     return self._inner_hookexec(hook, methods, kwargs)
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/pluggy/manager.py", line 61, in <lambda>
INTERNALERROR>     firstresult=hook.spec_opts.get('firstresult'),
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/pluggy/callers.py", line 201, in _multicall
INTERNALERROR>     return outcome.get_result()
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/pluggy/callers.py", line 76, in get_result
INTERNALERROR>     raise ex[1].with_traceback(ex[2])
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/pluggy/callers.py", line 180, in _multicall
INTERNALERROR>     res = hook_impl.function(*args)
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/_pytest/mark/__init__.py", line 156, in pytest_collection_modifyitems
INTERNALERROR>     deselect_by_mark(items, config)
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/_pytest/mark/__init__.py", line 144, in deselect_by_mark
INTERNALERROR>     if matchmark(item, matchexpr):
INTERNALERROR>   File "/home/hcs/.local/share/virtualenvs/pytest_repro-liG8mEsl/lib/python3.7/site-packages/_pytest/mark/legacy.py", line 69, in matchmark
INTERNALERROR>     return eval(markexpr, {}, MarkMapping.from_item(colitem))
INTERNALERROR>   File "<string>", line 1
INTERNALERROR>     a/
INTERNALERROR>      ^
INTERNALERROR> SyntaxError: unexpected EOF while parsing