unit testing - Making python COM client testable

Question

I have read about unit testing in python, but all examples I found are based on trivial examples of mocking objects. I have no idea how to really implement tests for the project in a way it can be tested without accessing COM port. project is mainly used for control of another application via COM API plus evaluating data produced by app and making reports, so let's say it is higher abstraction level api made as python library. COM interface is non-trivial, with main object that is exposing some managers, the managers exposing containers of objects, that are having references to another objects, so a web of conencted objects responsible for different things controlled application. Architecture of python library somehow follows the COM structure. During library import main COM object is dispatched and stored in central module, manager-level modules on import are getting references to COM manager objects from central module and then manager-level methods are using this COM manager objects in their methods. Examples for better understanding

#__init__
from managera import ManagerA
from centralobject import CentralObject
central_object = CentralObject()
manager_a = ManagerA()  #here all initialisation to make everything work,
manager_b = ManagerB()  #so full com object needed to import the package
...

#centalobject
class CentalObject():
    def __init__():
        self.com = Dispatch("application")
...

#managera
from project import central_object
class ManagerA():
    def __init__():
        self.com = central_object.com.manager_a
def manager_a_method1(x):
    foo = self.com.somecontainer[x].somemethod()
    foo.configure(3)
    return foo
...

In current state it is hard to test. It is even not possible import without connection to the COM app. Dispatch could be moved into some init function that is executed after the import, but I don't see how it would make the testing possible. One solution would be to make test double that have structutre similar to the original application, but for my unexperienced in testing mind it seems a bit overkill to do this in each method test. Maybe it is not and that's how it should be done, I am asking somebody's more experience advice. Second solutuon that came to my mind is to dispatch COM object every time any COM call is made, and then mock it but it seems a lot of dispatches and I don't see how it makes the code better. Tried also with managers not being defined as classes, but modules, however it seemed even more hard to test as then COM managers was refrerenced during module import, not object instantiation.

What should be done to make testing posible and nice without accessing COM? Interested in everything: solution, advice or just topic that I should read more about.

Answer 1

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