Adding Support for Tuple of Prefixes #306

Problem

In a project I am working on, I recently came across a need for referring to cases with differing prefixes. That is,

prefix1_id():
    pass

prefix2_id():
    pass

Present Solution

One could rename the case functions with a common prefix—e.g., case_prefix1... and case_prefix2.... However, this removes the customization of having support for custom prefixes in pytest_cases. Additionally, it would involve refactoring any pre-existing test code.

My Solution

After digging through the source code of pytest_cases, I modified a few lines to support tuples of prefixes:

First, I altered the validation code in get_all_cases() to support tuple[str].
pytest_cases/case_parametrizer_new.py::251

    # validate prefix
    if not isinstance(prefix, str):
        if not (isinstance(prefix, tuple) and all(isinstance(val, str) for val in prefix)):
            raise TypeError("`prefix` should be a string, found: %r" % prefix)
    if isinstance(prefix, tuple):
        # Reverse sort prefix to guarantee greedy prefix completion
        prefix = sorted(tuple, reverse=True)

Then, I modified get_case_id() to return the appropriate id when a tuple of prefixes is given.
pytest_cases/case_funcs.py::162

    if _id is None:
        # default case id from function name based on prefix
        if isinstance(prefix_for_default_ids, str):
            _id = case_func.__name__.removeprefix(prefix_for_default_ids)
        else:
            original = case_func.__name__
            for prefix in prefix_for_default_ids:
                modified_id = original.removeprefix(prefix)
                if not original == modified_id:
                    _id = modified_id
                    break

From my brief testing, the changes seem to cover all the use cases of prefix and performed as expected.

Usage:

@pytest_cases.parametrize_with_cases('case', prefix=('prefix1_', 'prefix2_')...)
def test_foo(case):
    pass

Proposal

Would support for tuples of prefixes be desirable behaviour for pytest_cases? If so, I would be more than happy to draft up a pull request and formalize these code changes with the appropriate refactors.