[metaphorm]

you're already writing the test cases to ensure correct behavior with typical input, and predictable exceptional input. putting in one more assert for predictable exceptional input (wrong type) doesn't really add a noticeable amount of overhead to writing the tests you were already writing.

[macspoofing]

>putting in one more assert for predictable exceptional input (wrong type) doesn't really add a noticeable amount of overhead

Yes. We call that 'typing'.

[discreteevent]

And it takes less typing (keyboard) than the assert, and you get free documentation inline with the code!