Code coverage in AX2012 R3


How is code coverage implemented for standard classes / Standard tables ?

For example, A standard class has 50 methods and one custom method is added . Now i need to create a test case class for the custom method that i added in the standard class .

To achieve 100 % code coverage should i write test case for all the 50 standard methods + 1 custom method in the class or is it enough to write just for the one custom method that was added ?

How is this scenario handled in Unit test framework in AX2012 R3 CU10 ?

Thanks & Regards,