Feature suggestions (C# Moq inspiration)

[Eldar1205]

Hi,

I looked at this open source library and want to say I really like the idea of finally having a type-hint oriented mocking library for Python so thank you! I'd like to suggest some features inspired by C# Moq library which looks very similar in design:

1. Add a matcher for custom predicate, e.g. even integers predicate every(function_mock).with_args(pred(lambda x: x % 2 == 0)).returns(True). In case of verifications, the error message can include the code of the predicate itself, would be very useful.
2. For returns add an option to return results based on a function of the input args, e.g. setup a function to return the negative of an integer: every(function_mock).returns(operator.neg) with def function_mock(param: int): pass