First, turn off ZeroLink for the application target you want to test. Just as with a framework, your unit tests will be built as a test bundle containing only the tests, completely separate from the code being tested. The test bundle will access the code in your application by linking against it, and you can't link against something built with ZeroLink. 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 application project. This is the target that will actually contain your tests. When you add the test bundle target, Xcode shows its Info window. In the General tab of this window, press the + button and choose your application target from the sheet that appears. This will make your test bundle target depend on your application target, so you can just build your test bundle all the time and have your application automatically rebuild first.
Now you actually need to make your test bundle link against your application. You do this using the Bundle Loader property under Linker Options in your test bundle target's configurations. You need to set the value of this option to the path of your application executable and not just its wrapper:
$(BUILT_PRODUCTS_DIR)variable is expanded at build time to be the path to the build products for the currently-selected configuration, which lets you avoid using an absolute path.
The final step is to tell the unit testing infrastructure how to run your tests. For a framework, the dynamic loader does the heavy lifting; when the test rig loads your test bundle, the loader will automatically load the frameworks it depends on including the one you're testing. However, for an application to be tested the application must be launched and the test bundle injected into it. You can specify that this should happen using the Test Host property under Unit Testing in your test bundle target's configurations. Just as with the Bundle Loader property, you need to set the value to the full path of your application executable. Since you've already done that once, you can just re-use the value of the Bundle Loader setting by specifying
$(BUNDLE_LOADER)— this is the underlying variable that the property is associated with.
Now just like with frameworks you can add test cases to your test bundle just by adding new files based on the Cocoa Objective-C test case class template. Your application code can remain in your application target and your unit testing code can remain in your test bundle target. Whenever you build your test bundle target, once everything is built your application will launch, its tests will be run, and it will quit — and the test results will be reported via the Build Results window just like compiler and linker errors.