I’m going to demonstrate today how to use ReSharper to quickly abstract even very large framework components. These might even be components that otherwise offer no abstract parent or interface with which to abstract their use as a dependency. This can be an important step to take when trying to properly unit test a given class or method.
We’ll begin by defining a wrapper class. Use the keyboard shortcut CTRL-ALT-INS to quickly and easily add a class.
Once this class has been generated we then build the class’ constructor. ALT-INS brings up the code generation menu. Select “Constructor…” from the menu.
We then add the Wrapper’s dependency, which is the object we’re trying to abstract, as a parameter to the constructor. ALT-Enter to accept adding the using statement.
ALT-INS to bring up the code generation menu quickly.
Then, using ReSharper, change this parameter to initialize a field which ReSharper will add. The keyboard shortcut here is ALT-Enter and then selecting the first option in the menu.
Now that the private field has been added we need to generate the Delegating Members of the Wrapper. ALT-INS brings up the code generation menu. Select ”Delegating Members…” from the menu.
Be sure to select the entire list of members which will generate a complete Wrapper class implementation.
Now that there’s a complete Wrapper class we’ll use the Refactor method to extract an abstract parent class. The keyboard shortcut for this is CTRL-SHIFT-R. Select “Extract Superclass…” from the menu.
Select all public methods on the class.
Then select all of the methods that were previously selected and make them abstract.
Finally, unselect the constructor method and move forward.
This will generate the base class, which is now a successful abstraction from the framework component that the Wrapper wraps. And the Wrapper will inherit from this base class.
Next we need a Factory to abstract the creation of this new Wrapper.
Build the Factory to use the Wrapper and return it.
Now give the Factory its own interface using the Refactor method. The keyboard shortcut for this is CTRL-SHIFT-R. Select “Extract Interface…” from the menu.
Again select all public methods for the interface members.
Generate the interface for the Factory for the final level of abstraction.
And finally consume the framework component from the abstracted class which is returned by the new Factory. The new Factory can be injected by most mocking frameworks since it’s abstracted by an interface.
By using this method, and relying on the Factory interfaces and abstract Wrapper base classes instead of the concrete objects, we better define our seams in our application and provide for true unit testing. And all while working around issues such as internal sealed classes and so forth that tend to be common enough in the framework so as to regularly cause a headache, especially with unit testing.