Unit testing is usually used for testing public types and members. However, there are cases when you might need to test types or members that are not public. These could be internal classes or private helper methods, for instance. Whether that is proper unit testing or beyond its scope is not a discussion that I want to get into here. However, in this post, I will show how you can unit test non-public types and members from .NET assemblies.
When faced with the need for testing non-public types and members you can use several approaches:
- change the accessibility to public; you can do that perhaps only for debug builds and keep the intended accessibility in release builds by using conditional compilation.
- provide public members of a class that invoke private ones;
- use reflection.
The first solutions involve changing the API only for the sake of the testing. The last solution avoids that but requires more work. To help with that, the Visual Studio unit testing framework provides some helper types that enable you to focus on the actual testing and be less concerned about the reflection details.
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