mocking for testing introduction testing software systems is not an easy thing to dothe functionsobjectsmethods etc that are involved in any program can be complex things in their own right in many cases they depend on and interact with other functionsmethods and objectsvery few functions and methods operate in isolation thus the success of failure of function or method or the overall state of an object is dependent on other program elements howeverin general it is lot easier to test single unit in isolation rather than to test it as part of larger more complex system for examplelet us take python class as single unit to be tested if we can test this class on its own we only have to take into account the state of the classes object and the behaviour defined for the class when writing our test and determining appropriate outcomes howeverif that class interacts with external systems such as external servicesdatabasesthird party softwaredata sources etc then the testing process becomes more complex(cspringer nature switzerland ag huntadvanced guide to python programmingundergraduate topics in computer science