added unit tests

[gsailer]

Writing unit tests for config and api as in #3
I am submitting a work in progress. For now only the config tests are written.
I would really appreciate some feedback on the tests so far.

[femueller]

Hey @sublinus - thanks for the submission!

When testing the PR I was trying to execute the test like I am used to from the root directory.

That caused the problem that the test_creds.yml file is not readable from that path and should be from my perspective become more flexible so that you can either execute it from the root or tests directory.

What's your opinion on this?

That's what happens to me when executing it from the root directory:

pytest tests/.
=========================================================================================== test session starts ============================================================================================
platform darwin -- Python 3.5.0, pytest-4.0.2, py-1.7.0, pluggy-0.8.0
rootdir: /Users/femueller/git/tmp/python-n26, inifile:
collected 2 items

tests/test_config.py .F                                                                                                                                                                              [100%]

================================================================================================= FAILURES =================================================================================================
________________________________________________________________________________________________ test_file _________________________________________________________________________________________________

monkeypatch = <_pytest.monkeypatch.MonkeyPatch object at 0x1047740f0>

    @mock.patch.dict(os.environ, {"N26_USER": "", "N26_PASSWORD": "", "N26_CARD_ID": ""})
    def test_file(monkeypatch):
        # patch path to local test file
        def mockreturn(path):
            return "./test_creds.yml"
        monkeypatch.setattr(os.path, "expanduser", mockreturn)
>       assert config.get_config() == config.Config(username='john.doe@example.com',
                                                    password='$upersecret', card_id="123456789")

tests/test_config.py:17:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

    def get_config():
        # try to get values from ENV
        username, password, card_id = [os.environ.get(e)
                                       for e in ["N26_USER", "N26_PASSWORD", "N26_CARD_ID"]]

        if not username or not password or not card_id:
            # print('Environment variables not set. trying to load cfg')

            config_file = os.path.expanduser('~/.config/n26.yml')
>           with open(config_file, 'r') as ymlfile:
E           FileNotFoundError: [Errno 2] No such file or directory: './test_creds.yml'

../../../.pyenv/versions/3.5.0/lib/python3.5/site-packages/n26/config.py:17: FileNotFoundError
==================================================================================== 1 failed, 1 passed in 0.10 seconds ====================================================================================

[gsailer]

Thanks a lot for the feedback @femueller.
I see the problem with the non-relative file path and changed it to a relative path. Additionally I created a new test for prerequisites, so that it is easier to see why tests failed if the "test_creds.yml" is missing for some reason.

Further I also added a new build target in the Makefile, which uses the "pipenv run" command to make sure the pytest from the project virtual environment is used.
I will continue with the testing of the api soon.

[femueller]

Great! Thanks for addressing it so quickly!

I will merge your contribution and for future submissions, I would suggest creating a new PR.