Investigate adding more automated tests

[tvhong]

The automated tests available for this add-on is quite minimal. We want to add more automated tests to prevent regressions.

Let's use this issue to start the investigation.

Acceptance Criteria:

• Have a good understanding of which part of the add-on could be tested, and how much effort it would take.
• Document the findings here.

[tvhong]

I saw this this pytest-anki by glutanimate in https://github.com/artyompetrov/AutoDefine_oxfordlearnersdictionaries/blob/master/tests/tests.py .

We might be able to use it. But beware that there might be some problems running pytest-anki on MacOS.

[tvhong]

More tests would have prevented issues such as: https://github.com/tvhong/incremental-reading/issues/18