Support `__test__` attribute in PyTest test discovery

A recent release included support for alternative (i.e. non-"test") test prefixes.

Pytest, also uses a custom __test__ dunder when discovering tests: python.py#L349. I.e. any function with the attribute __test__ = True is considered a test regardless of its prefix. Currently, this library does not support this dunder.

Would it be possible to support the __test__ dunder in the recently added is_pytest_test method?

I am happy to work on this unless someone else sees a quick fix.

Suggested Fix

An additional test in the StackFrameNamer class for the __test__ dunder could be something like the following:

@staticmethod
def _is_marked_with_test_dunder(
      method_name: str,
      frame_globals: dict[str, "Any"],
) -> bool:
    function = frame_globals.get(method_name)
    return (
          function is not None
          and hasattr(function, "__test__")
          and getattr(function, "__test__") is True  # i.e. True not truthy
    )

@staticmethod
def is_pytest_test(frame: FrameInfo) -> bool:
    method_name = frame[3]
    frame_globals = frame.frame.f_globals
    patterns = PytestConfig.test_naming_patterns
    return (
          StackFrameNamer._is_match_for_pytest(method_name, patterns)
          or StackFrameNamer._is_marked_with_test_dunder(
                method_name,
                frame_globals,
          )
    )

Here, the function name is looked up in the frame globals, and if found, it checks for the __test__ dunder. I would need to refresh my memory on Python's FrameInfo to check whether this is the best way of doing this.

Start in approvaltests/namer/stack_frame_namer.py at StackFrameNamer.is_pytest_test and review the existing discovery tests for that class. Add coverage for functions whose test attribute is exactly True, then run the relevant test suite and confirm those functions are recognized regardless of their name prefix.