One common issue of team development is sharing configuration files. If a developer is testing something out and changes a value and then accidentally checks that file in it affects all developers.

There are a few approaches to solving this issue:
1) Be very careful and disciplined.
2) Have a web.config.template under source control that developers copy to web.config and not include in source control.
3) Have a build script task to generate a config file on demand.
4) What we are trying. Unit test the configuration to make sure it is correct.
+web.config is under source control
+changes are caught by a test. If it is meant to be distributed to all developers then the test should be updated as well
-have to write a test for the configuration (not a big minus in my opinion)
-If you have different config settings for the test project than the actual project then this will not work

In order to test a config file though we need to be able to load that config file! In our case we are testing a web.config and nunit is expecting a app.test.dll.config file. The easy way around this was to copy the web.config from our application to the proper folder and name with a pre-build event:

copy $(SolutionDir)\App.Service\web.config $(ProjectDir)\bin\App.Test.dll.config /y

Now my tests use that config file to assert that the settings are proper. The big downside to this approach is that it will overwrite the app.config file that you may already have for your test which may not be desirable.

Alternatives:
1) Parse the XML of the config file you want to test and verify
2) Load and unload and external config file in a test (I started with this and could not get it to work)