Add test that involves accessing the MongoDB database

[eecavanna]

In #74, we introduced the first set of tests that involve the API. None of those tests—and, indeed, none of the tests in the repo today—involve the MongoDB database, though. For example, there is no test that visits /health and confirms the API response says the MongoDB database is accessible.

This ticket represents the task of adding at least one test to our test suite, that involves accessing the MongoDB database.

I suggest working on #53 at roughly the same time.