It's straightforward to write unit tests for Objective-C Cocoa frameworks with Xcode 2.1 and later.
First, turn off ZeroLink when building your framework. ZeroLink is a great technology, but you can't link against something that's built with ZeroLink, and that's exactly what your unit tests are going to do. Note: You only need to do this for Xcode 2.1 through Xcode 2.5. Xcode 3.0 removed support for ZeroLink, since the linker is now sufficiently fast as to obviate it.
Next, add a new Cocoa Unit Test Bundle target to your framework project. This is the target that will actually contain your tests.
When you add the new test bundle target Xcode should bring up its Info window. Switch to its General tab and press the + button in the lower-left to add a new dependency. In the resulting sheet, choose your framework target. This tells the build system that your framework target needs to be built before your test bundle target.
Now that you've declared the dependency between the targets, you need to make sure your test bundle actually links against your framework. Make your test bundle target the active target by choosing it from the Project > Set Active Target submenu. Then highlight the Products group in the Groups & Files view at the left of the Xcode project window. In the detail view to the right, you'll see all of the products that are built by the various targets in your project; one of the rows will be for your framework. Click the checkbox at the very right of its row, in the Target Membership column, to make your test bundle link against your framework.
Now you can add test cases to your test bundle by just adding new files based on the Cocoa Objective-C test case class template. You don't need to add any of your framework code to your test bundle, and you don't need to add any testing code to your framework. And you're not restricted to using only header files with public visibility in tests, either; you should be able to use anything from your framework target, so long as it's exported at link time.
- Xcode: Unit Testing Cocoa frameworks