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Mocking a COM object RRS feed

  • Question

  • I have an application which is using a COM object which is implemented as an exe (actually a full fledged application with GUI, file system persistence and all). Type library is embedded in the exe file.

    I need to unit test my code and to avoid using the real COM object, I would like to use what I believe is a mock object instead.

    Is it possible to create such a mock object (manually, "hand-rolled" or by Visual Studio 2015) directly (which then implements the COM interface) without explicit specifying a "replica" of the COM interface and implement another layer of abstraction using this interface ?

    I guess this sounds quite vague, I am pretty new to unit testing, mocking etc. and I believe this should be a simple thing that I just oversee due to my lack of knowledge (the lack of knowledge is perhaps actually more related to COM interop than mocking)

    Wednesday, February 3, 2016 9:37 AM

Answers

All replies

  • Seems like I found out.

    Visual Studio confused me by showing the external COM Object (say its named MyComClassClass in object browser) implementing an interface called MyComClass which showed as empty.

    However, a hidden interface called IMyComClass contains all methods etc. and seems to be useful for mocking.

    The real names obscured for discretion :)

    I have seen this before (that the class exposes members, but the interface which the class is inherited from does not).
    I don't know the reason for this, is this a property of VS or the COM class tlb ?

    Wednesday, February 3, 2016 7:32 PM
  • Thanks for sharing the useful information here, EuroEager!

    >>I don't know the reason for this, is this a property of VS or the COM class tlb ?

    My understanding is that it would be related to the COM class tlb.

    Reference:

    https://social.msdn.microsoft.com/Forums/vstudio/en-US/d24b9590-5651-4a2b-be81-5d58584dd3b3/com-iid-of-a-class?forum=netfxbcl

    Thanks,

    Jack


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    Thursday, February 4, 2016 9:06 AM