I spent almost two hours on a unit test issue yesterday, walking away with the issue unresolved and myself frustrated. I came back to it this morning and fixed it in 2 minutes. Remember, you don’t always need a mock library to create fakes.
The Task at Hand
In the process of removing some obsolete warnings from our builds, I came across a few areas where the change was less than trivial. Before making the changes, I decided it would be a good idea to write some unit tests to ensure that my changes did not affect functionality.
The class to be tested, however, took
IConfiguration in the constructor. Our current project does not make use of the Options pattern in .Net Core, meaning anything that needs configuration values has to carry around a reference to
IConfiguration and then extract the values manually. Yes, I will want to change that, but not right now.
So, in order to write these unit tests, I had to create a mock of
IConfiguration that returned the values this class needed. Our project currently uses Telerik JustMock, so I figured it would be a fairly easy task to mock. However, I ran into a number of problems that had me going down the path of creating multiple mock classes for different interfaces, including
IConfigurationSection. I immediately thought “There has to be a better way.”
The Better Way
Some quick Google research led me to this gem of a post on StackOverflow. In all my time with .Net configuration, I never knew about or used the
AddInMemoryCollection extension. And that led me to the simplest solution: create an “real boy” instance of
IConfiguration with the properties my class needs, and pass that to the class in testing.
I suppose this is “dumb mocking” in the sense that it doesn’t use libraries written and dedicated to mocking objects. But it gets the job done in the simplest method possible.