add python type hints via pyre infer to tests/

[edward-io]

What does this PR do?

automatically adds python type hinting using pyre to tests.

manually fixed some broken areas.

breaking this up into multiple PRs to make it easier to review.

Does your PR introduce any breaking changes? If yes, please list them.

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[carmocca]

We aren't interested in adding typing to tests. The type checker is not configured to run over them.

Tests will naturally fail if types are not correct. Typing is most useful for users but tests are internal to the project.

[Borda]

@edward-io do you think this could be used for the package instead to fill some of the missing typing? 🐰

[edward-io]

@carmocca Typing helps beyond correctness in tests - it helps with autocomplete in text editors and provides self-documentation for easier readability as well :) If we don't think that the benefits outweigh the costs, I can go ahead and close this PR.

@Borda - #11956 #11955, I'll add another one for the main library as well.

[carmocca]

@edward-io Sorry if I sounded too harsh with my previous comment! Let me elaborate.

Mypy is not configured to run over the test directory:

https://github.com/PyTorchLightning/pytorch-lightning/blob/25b505508d376d87103a592f23f7c9b0a602d12e/pyproject.toml#L26

So I would not be comfortable adding type information if it's not going to be checked. The cost of running the bot is negligible, however, adding types without the checker is like adding code without tests.

Considering that there is still a lot of the source code still untyped, I would focus on that. Maybe one day it's worth adding type annotations for tests but it's very low value and the test suite is already very fragmented.

I'll add another one for the main library as well.

For other typing PRs to the codebase, you should aim to remove entries from:

https://github.com/PyTorchLightning/pytorch-lightning/blob/25b505508d376d87103a592f23f7c9b0a602d12e/pyproject.toml#L45-L98

but keep in mind that each PR should address only one or a few files. You can see examples in the linked PRs to #7037