Opt test out of SPM

Author: kyleve

WorkflowUI/Tests/XCTestCase+Extensions.swift

@@ -24,7 +24,11 @@ extension XCTestCase {
         test: (ViewController) throws -> Void
     ) rethrows {
         guard let rootVC = UIApplication.shared.delegate?.window??.rootViewController else {
-            XCTFail("Cannot present a view controller in a test host that does not have a root window.")
+            #if SWIFT_PACKAGE
+                print("WARNING: Test cannot run in SPM, it requires an app host. Please run WorkflowUI.podspec's tests.")
+            #else
+                XCTFail("Cannot present a view controller in a test host that does not have a root window.")
+            #endif
             return
         }