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 discovered my problem was that I had 'Link time optimisation' enabled on my debug build. Setting it to no resolved the problem.