feat(ios): algorithm to determines UserDefaults delta

ios/engine/KMEI/KeymanEngineTests/KeymanEngineTests.swift

@@ -23,6 +23,29 @@ class KeymanEngineTests: XCTestCase {
     // Put teardown code here. This method is called after the invocation of each test method in the class.
   }
 
+  func getAssignedDictionary(for userDefaults: UserDefaults) -> [String: Any] {
+    var currentDictionary = userDefaults.dictionaryRepresentation()
+    clearSettings(of: userDefaults)
+    let baseDict = userDefaults.dictionaryRepresentation()
+
+    baseDict.forEach({ pair in
+      currentDictionary.removeValue(forKey: pair.key)
+    })
+
+    // The return value is now properly constructed.  Now to put the defaults back in place before we leave.
+    //userDefaults.register(defaults: currentDictionary) // adds them in an unclearable way!
+    currentDictionary.forEach({ pair in
+      userDefaults.set(pair.value, forKey: pair.key)
+    })
+    return currentDictionary
+  }
+
+  func clearSettings(of userDefaults: UserDefaults) {
+    let domain = Bundle.main.bundleIdentifier!
+    userDefaults.synchronize()
+    userDefaults.removePersistentDomain(forName: domain)
+  }
+
   func testStorageAccess() {
     // Xcode unit tests cannot use capabilities, and thus we cannot access a true app group.
     // So, we'll use a sandboxed analogue for this instead.
@@ -31,8 +54,10 @@ class KeymanEngineTests: XCTestCase {
     let storage = Storage.active!
     log.info(storage.baseDir)
 
+    // Diff-magic for determining the dictionary to be utilized for a test.
     let userDefaults = storage.userDefaults
-    let dictionary = userDefaults.dictionaryRepresentation()
+    userDefaults.set(4, forKey: "testEntry")
+    let dictCheck = getAssignedDictionary(for: userDefaults)
 
     Storage.active.erase()
   }