TST: Extract methods from TestXMySQL and TestXSQLite and remove

[TomAugspurger]

I haven't looked too closely, but in https://github.com/pandas-dev/pandas/pull/13611/files the TestXMySql tests were unconditionally skipped.

IIUC, these are the test using a DBAPI2 Connection object, which is deprecated? We should remove these tests if they aren't being run.

[jorisvandenbossche]

IIUC, these are the test using a DBAPI2 Connection object, which is deprecated?

It's no longer deprecated, but actually removed (for mysql writing) or accepted (for sqlite, and in practice also for reading query's)

We should remove these tests if they aren't being run.

Yeah, IIRC those tests were old tests from before the sqlalchemy refactor, and kept for "we should actually clean up the tests (go through them, and keep the useful bits in case it is not yet covered in the other tests), but that is some work, so just leave them there for now" reasons

[TomAugspurger]

Gotcha, so the TODO here is to pick out the interesting tests, and move them to the _TestMySQLAlchemy class?:

[jorisvandenbossche]

Yep (but it might be there is actually nothing interesting)

[jorisvandenbossche]

And the same is true actually for TestXSQLite (which is not skipped), also for those it would be nice to better integrate them with the rest of the tests

[TomAugspurger]

One potential strategy for discovering which lines are tested in just TestX*:

1. Run just the TestSQLiteAlchemy tests with covereage
2. Run just the TestXSQLite tests with coverage

dif the two coverage reports (not sure if there's a tool to do this, or if you would do it manually).