In case there is a need to reset to the original function in the test, the next AxUnit.Mocking.Mockcall is necessary where by the mockeeFn and mockFn parameters are the same function names.
In following example the mock setup of Siemens.Simatic.S71500.Clocks.GetOperatingTime is reseted.
AxUnit.Mocking.Mock('Siemens.Simatic.S71500.Clocks.GetOperatingTime', 'Siemens.Simatic.S71500.Clocks.GetOperatingTime');