WIP - Adding tests + testing healthcheck

[machikoyasuda]

WIP WIP! - Made this PR to ask a question:

Having trouble importing app into the tests. I tried adding an test/__init__.py file which returns this error:

====================================================== ERRORS ======================================================
________________________________________ ERROR at setup of test_healthcheck ________________________________________

app = <function app at 0x7fbedf8b2550>

    @pytest.fixture
    def client(app):
        """A test client for the app."""
>       return app.test_client()
E       AttributeError: 'function' object has no attribute 'test_client'

tests/conftest.py:12: AttributeError

Removing that test/__init__.py file gets this error:

ImportError while loading conftest '/home/calitp/app/tests/conftest.py'.
tests/conftest.py:3: in <module>
    from app import app as flask_app
E   ModuleNotFoundError: No module named 'app'