Unit testing the app.config file with NUnit

Question

When you guys are unit testing an application that relies on values from an app.config file? How do you test that those values are read in correctly and how your program re

Answer 1

The simplest option is to wrap the methods that read configuration such that you can substitute in values during testing. Create an interface that you use for reading config and have an implementation of that interface get passed in as a constructor parameter or set on the object as a property (as you would using dependency injection/inversion of control). In the production environment, pass in an implementation that really reads from configuration; in the test environment, pass in a test implementation that returns a known value.

If you don't have the option of refactoring the code for testability yet still need to test it, Typemock Isolator provides the ability to actually mock the .NET framework configuration classes so you can just say "next time I ask for such-and-such appSettings value, return this known value."