How to add framework reference to a framework from a different project

Question

I using Cocoapods/xcodeproj gem to generate my Xcode projects, for a framework in the same project I can do

common = project.targets.find { |t| t.name == "TestCommon" }  
target.frameworks_build_phases.add_file_reference(common.product_reference)

But this doesn't work if framework and the target are from separate projects but in the same workspace.