Problem

If you would like to create framework, which will be used only in unit tests. At one moment you will need to import XCTest. But Xcode will give you awesome error:

"Cannot load underlying module for XCTest"

Reason

As I understand, Xcode doesn't know that your framework will be imported only in test target, so it can't find XCTest framework in "normal" framework location.

Solution

Add to your config file:

OTHER_LDFLAGS = -weak_framework XCTest -weak-lswiftXCTest
FRAMEWORK_SEARCH_PATHS = $(DEVELOPER_FRAMEWORKS_DIR) $(PLATFORM_DIR)/Developer/Library/Frameworks
ENABLE_BITCODE = NO // XCTest doesn't support bitcode, why would it?

It will provide location for XCTest framework and link it to your project.