Don’t make it any harder than it has to be—read the friendly manual.
I spent a little time trying to get some test cases working where the code depended on the .config file. Now, a typical unit test suite is library assembly—a .dll. As such, if you give it an app.config file, Visual Studio will not copy and rename it like it will for .exe’s. You must make that happen yourself. Since you don’t want to check in the bin/debug directory, you need to specify a “Pre-build event command line.”
copy $(ProjectDir)app.config $(ProjectDir)$(OutDir)$(TargetFileName).config