A quick intro

Given some class (the implementation of its method is not relevant)

class MyThing:

    def multiple_arg(self, prefix: str, number: int) -> str:
        pass

Mock and Verify

We con mock behaviour and verify interactions as follows:

from typemock import tmock, when, verify

expected_result = "a string"

with tmock(MyThing) as my_thing_mock:
    when(my_thing_mock.multiple_arg("p", 1)).then_return(expected_result)

actual = my_thing_mock.multiple_arg(
    number=1,
    prefix="p"
)

assert expected_result == actual
verify(my_thing_mock).multiple_arg("p", 1)

Things to note:

• The mocked object must be used as a context manager in order to specify behaviour.
• You must let the context close in order to use the defined behaviour.

Type safety

And when we try to specify behaviour that does not conform to the contract of the object we are mocking

expected_result = "a string"

with tmock(MyThing) as my_thing_mock:
    when(my_thing_mock.multiple_arg(prefix="p", number="should be an int")).then_return(expected_result)

We get an informative error such as:

typemock.safety.MockTypeSafetyError: Method: multiple_arg Arg: number must be of type:<class 'int'>

Things to note:

• You will also get type hint errors if you attempt to specify behaviour that returns the incorrect type.