.net - 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 reacts to incorrect values entered into a config file?

It would be ridiculous to have to modify the config file for the NUnit app, but I can't read in the values from the app.config I want to test.

Edit: I think I should clarify perhaps. I'm not worried about the ConfigurationManager failing to read the values, but I am concerned with testing how my program reacts to the values read in.

Answer 1

I usually isolate external dependencies like reading a config file in their own facade-class with very little functionality. In tests I can create a mock version of this class that implements and use that instead of the real config file. You can create your own mockup's or use a framework like moq or rhino mocks for this.

That way you can easily try out your code with different configuration values without writing complex tests that first write xml-configuration files. The code that reads the configuration is usually so simple that it needs very little testing.