The fix for the database locking bug was to have a singleton
`DBHelper` instance. This breaks tests because multiple tests
share the same database. The solution is to:
* Hack together a static method which clears the singleton,
then invoke it in the `setUp()` method for relevant test cases.
* Ensure the mock context provided to the providers during
the tests is able to provide a context via `getApplicationContext()`.
Without this, the mock context throws an `UnsupportedOperationException`
when invoking this method.
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