Unit tests for diff take 25 seconds

[dmpetrov]

Description

Our unit test suite becoming supper slow (lib unit-test time takes 58 seconds!) and useless as a result (now I cannot run it for every change I do - which works just fine before).

We need to reduce it's unit-tests run-time significantly (5-10 times).

I see multiple anti-patterns but I'm sure there are more:

1. Too many pytest.mark.parametrize

The test below generates 50+ tests without a good reason. For example - there is not need to test save() in diff test - tests have to be "orthogonal". It needs to be replaced by 7-15 smaller tests.

@pytest.mark.parametrize("added", (True, False))
@pytest.mark.parametrize("deleted", (True, False))
@pytest.mark.parametrize("modified", (True, False))
@pytest.mark.parametrize("same", (True, False))
@pytest.mark.parametrize("status_col", ("diff", None))
@pytest.mark.parametrize("save", (True, False))
def test_compare(test_session, added, deleted, modified, same, status_col, save):
    ...

2. Touching cloud resources

It looks like test_resolve_file() and such require access to clouds.

E               pytest_servers.exceptions.RemoteUnavailable: gs: Failed to setup mock remote: Error while fetching server API version: ('Connection aborted.', FileNotFoundError(2, 'No such file or directory'))

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