Fix: DataStore E2E Integration Tests (#596)

* fix e2e integration test

* Make sure only cast as Post event and added a explanation comment

Author: ruiguoamz

Amplify.xcodeproj/project.pbxproj

@@ -38,15 +38,20 @@ class DataStoreEndToEndTests: SyncEngineIntegrationTestBase {
         let hubListener = Amplify.Hub.listen(
             to: .dataStore,
             eventName: HubPayload.EventName.DataStore.syncReceived) { payload in
-                guard let mutationEvent = payload.data as? MutationEvent,
-                    let post = try? mutationEvent.decodeModel() as? Post
+                guard let mutationEvent = payload.data as? MutationEvent
                     else {
                         XCTFail("Can't cast payload as mutation event")
                         return
                 }
 
+                // This check is to protect against stray events being processed after the test has completed,
+                // and it shouldn't be construed as a pattern necessary for production applications.
+                guard let post = try? mutationEvent.decodeModel() as? Post, post.id == newPost.id else {
+                    return
+                }
+
                 if mutationEvent.mutationType == GraphQLMutationType.create.rawValue {
-                    XCTAssertEqual(post.content, post.content)
+                    XCTAssertEqual(post.content, newPost.content)
                     XCTAssertEqual(mutationEvent.version, 1)
                     createReceived.fulfill()
                     return
@@ -109,15 +114,20 @@ class DataStoreEndToEndTests: SyncEngineIntegrationTestBase {
         let hubListener = Amplify.Hub.listen(
             to: .dataStore,
             eventName: HubPayload.EventName.DataStore.syncReceived) { payload in
-                guard let mutationEvent = payload.data as? MutationEvent,
-                    let post = try? mutationEvent.decodeModel() as? Post
+                guard let mutationEvent = payload.data as? MutationEvent
                     else {
                         XCTFail("Can't cast payload as mutation event")
                         return
                 }
 
+                // This check is to protect against stray events being processed after the test has completed,
+                // and it shouldn't be construed as a pattern necessary for production applications.
+                guard let post = try? mutationEvent.decodeModel() as? Post, post.id == newPost.id else {
+                    return
+                }
+
                 if mutationEvent.mutationType == GraphQLMutationType.create.rawValue {
-                    XCTAssertEqual(post.content, post.content)
+                    XCTAssertEqual(post.content, newPost.content)
                     XCTAssertEqual(mutationEvent.version, 1)
                     createReceived.fulfill()
                     return
@@ -171,16 +181,21 @@ class DataStoreEndToEndTests: SyncEngineIntegrationTestBase {
         let conditionalReceived = expectation(description: "Conditional save failed received")
 
         let hubListener = Amplify.Hub.listen(to: .dataStore) { payload in
-            guard let mutationEvent = payload.data as? MutationEvent,
-                let post = try? mutationEvent.decodeModel() as? Post
+            guard let mutationEvent = payload.data as? MutationEvent
                 else {
                     XCTFail("Can't cast payload as mutation event")
                     return
             }
 
+            // This check is to protect against stray events being processed after the test has completed,
+            // and it shouldn't be construed as a pattern necessary for production applications.
+            guard let post = try? mutationEvent.decodeModel() as? Post, post.id == newPost.id else {
+                return
+            }
+
             if payload.eventName == HubPayload.EventName.DataStore.syncReceived {
                 if mutationEvent.mutationType == GraphQLMutationType.create.rawValue {
-                    XCTAssertEqual(post.content, post.content)
+                    XCTAssertEqual(post.content, newPost.content)
                     XCTAssertEqual(mutationEvent.version, 1)
                     createReceived.fulfill()
                     return