xcode 4 fails to initiate unit tests (with linker error) after I created a new scheme

Question

My unit tests worked fine in xcode4 until I had to create a new schema to compile a package to run on my device for testing.

All I did was creating a new Target an

Answer 1

I've also run across problems with Xcode 4 after adding a target to an existing project. I eventually figured out that the Xcode DerivedData for the project was damaged. By deleting that data, I caused Xcode to rebuild the data and the project returned to normal. I found the data in my home Library folder (~/Library/Developer/Xcode/DerivedData/).