STYLE pre-commit check to ensure that test functions name starts with test

[MarcoGorelli]

In #50378, I found a test which isn't run in CI because its name doesn't start with test (as required by pytest)

I'm sure there's more

To find them, I think we need some AST which checks files in pandas/tests, which:

• have names not starting with test
• aren't decorated (else they might be fixtures)
• aren't used anywhere else inside that file (else they might be helper functions)

[MarcoGorelli]

we need to do this for classes too

[MarcoGorelli]

some more examples of tests which don't run (in addition to those posted in other issues)

pandas/pandas/tests/computation/test_eval.py

Lines 356 to 364 in 4e4be0b

	def check_single_invert_op(self, lhs, engine, parser):
	# simple
	try:
	elb = lhs.astype(bool)
	except AttributeError:
	elb = np.array([bool(lhs)])
	expected = ~elb
	result = pd.eval("~elb", engine=engine, parser=parser)
	tm.assert_almost_equal(expected, result)

pandas/pandas/tests/io/test_feather.py

Lines 116 to 119 in e38daf0

	def read_columns_different_order(self):
	# GH 33878
	df = pd.DataFrame({"A": [1, 2], "B": ["x", "y"], "C": [True, False]})
	self.check_round_trip(df, columns=["B", "A"])

so yeah, really need an automated check for this. on it