Add cassettes and modify testing to enable testing without internet

[ajakk]

This is unfinished and will still be modified a bit, but it is a good proof-of-concept for what I'm trying to do. tests/conftest.py has a pytest fixture in it which automatically handles logic related to vcrpy. Simply adding the argument vcr to any function will enable vcrpy for the function and will use/create the cassette with the function name in the cassette directory. With test classes, it is slightly more complex to use fixtures in class methods, and for this reason I added a class called FixtureInjector using an example from pytest docs. Further, this simplifies the use of vcr cassettes by not requiring function decorators with the correct path for every function you want to use cassettes for, which results in less work to use vcrpy.

Excluding the cassette directory, this commit currently adds 49 lines and removes 15 across tests/conftest.py and tests/test_buku{,Db}.py. I did some execution time testing as well by executing the command pytest tests/test_buku.py tests/test_bukuDb.py on the HEAD commit of both my and your repositories, 5 times each. Using the time returned by pytest, the average for your repository was 275.29 seconds, and the average in my repository was 59.19 seconds. In other words, using cassettes for the functions in these two test files sped up the test execution time by several minutes on my machine. This variability is completely attributed to the lack of network-related hangs during testing using the modifications in my repository.

Please keep in mind this is a work in progress and I still have some cleaning up to do with it, should you be interested in these changes.

[ajakk]

I see CI doesn't like the long filenames. Truncating them wouldn't be hard to implement.

[jarun]

We discussed that we can't allow so many new files. Are you planning to rework that?

[ajakk]

If it were a single file you'd never be able to re-record a single test on its own. That's a maintenance headache in a way multiple files aren't, and there's no reason for it. Materially, what is the problem with multiple files? Maybe I can mitigate your concern.

[jarun]

what is the problem with multiple files?

We discussed this already. I do not want to make the project littered with unnecessary files just for 1 platform. I appreciate your effort but this is just something I do not want to do. Thanks for your understanding.

[ajakk]

The benefits exist for everyone who runs the tests, regardless of platform. The number of files has no real effect on anything. It's really just a bonus that it makes the tests work better on Gentoo.