Conflict with pytest-black

[optimalstrategy]

Hello!

The plugin seems to be in conflict with pytest-black, a pytest integration for the Black code formatter. Here is what I get when I try to use pytest-azurepipelines and pytest-black simultaneously:

Click to see the log

```bash $ pytest --black ============================================================================================ test session starts ============================================================================================ platform linux -- Python 3.7.3, pytest-4.4.0, py-1.8.0, pluggy-0.9.0 rootdir: /home/george/github/test-project plugins: black-0.3.5, azurepipelines-0.6.0 collecting ... INTERNALERROR> Traceback (most recent call last): INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/_pytest/main.py", line 209, in wrap_session INTERNALERROR> session.exitstatus = doit(config, session) or 0 INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/_pytest/main.py", line 248, in _main INTERNALERROR> config.hook.pytest_collection(session=session) INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/pluggy/hooks.py", line 289, in __call__ INTERNALERROR> return self._hookexec(self, self.get_hookimpls(), kwargs) INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/pluggy/manager.py", line 68, in _hookexec INTERNALERROR> return self._inner_hookexec(hook, methods, kwargs) INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/pluggy/manager.py", line 62, in INTERNALERROR> firstresult=hook.spec.opts.get("firstresult") if hook.spec else False, INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/pluggy/callers.py", line 208, in _multicall INTERNALERROR> return outcome.get_result() INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/pluggy/callers.py", line 80, in get_result INTERNALERROR> raise ex[1].with_traceback(ex[2]) INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/pluggy/callers.py", line 187, in _multicall INTERNALERROR> res = hook_impl.function(*args) INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/_pytest/main.py", line 258, in pytest_collection INTERNALERROR> return session.perform_collect() INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/_pytest/main.py", line 497, in perform_collect INTERNALERROR> session=self, config=self.config, items=items INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/pluggy/hooks.py", line 289, in __call__ INTERNALERROR> return self._hookexec(self, self.get_hookimpls(), kwargs) INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/pluggy/manager.py", line 68, in _hookexec INTERNALERROR> return self._inner_hookexec(hook, methods, kwargs) INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/pluggy/manager.py", line 62, in INTERNALERROR> firstresult=hook.spec.opts.get("firstresult") if hook.spec else False, INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/pluggy/callers.py", line 208, in _multicall INTERNALERROR> return outcome.get_result() INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/pluggy/callers.py", line 80, in get_result INTERNALERROR> raise ex[1].with_traceback(ex[2]) INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/pluggy/callers.py", line 187, in _multicall INTERNALERROR> res = hook_impl.function(*args) INTERNALERROR> File "/home/george/.envs/test-env/lib/python3.7/site-packages/pytest_azurepipelines.py", line 28, in pytest_collection_modifyitems INTERNALERROR> parent = item.parent.obj # Test class/module INTERNALERROR> AttributeError: 'Session' object has no attribute 'obj' ##vso[results.publish type=JUnit;runTitle='Pytest results';]/home/george/github/test-project/test-output.xml ```

Steps to reproduce:

• Install pytest-black==0.3.5 and pytest-azurepipelines==0.6.0
• Run pytest with the --black flag: pytest --black

pytest-black uses a custom item class which does not define .obj attribute, leading to the error above. This PR adds attribute checks to pytest_collection_modifyitems() so the invalid items get skipped.

[tonybaloney]

Thanks!