Add tests to prove that the methods of every class do not change something inplace

[Marsmaennchen221]

Is your feature request related to a problem?

Currently there are almost no tests that test weather the methods do not change values inplace.

Desired solution

Add tests to test this behaviour for every inplace method.
If there are functions that change values inplace: change the behaviour so that the methods do not change values inplace.

Possible alternatives (optional)

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Additional Context (optional)

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[Marsmaennchen221]

You could a decorator like this:

def inplace_decorator(function):
    @functools.wraps(function)
    def run_test_with_inplace_check(*args, **kwargs):
        copy_dict = deepcopy(kwargs)
        function(*args, **kwargs)
        assert copy_dict == kwargs, f"Function {function.__qualname__} changes its arguments"

    return run_test_with_inplace_check

With a test you could implement it like this:

@pytest.mark.parametrize(
    ...
)
@inplace_decorator
def test_something(...):
    # test your code

This test will provide the error of a test first. After you fix the error it will fail the text if the parameter change within the test.