def copy_method(request):
    """
    Fixture to test both the old/deprecated `copy` and new `model_copy` methods.
    """
    if request.param == 'copy':
        return deprecated_copy
    else:

        def new_copy_method(m, *, update=None, deep=False):
            return m.model_copy(update=update, deep=deep)

        return new_copy_method

    Fixture to test both the old/deprecated `copy` and new `model_copy` methods.
    
tests/test_construction.py