Fix main thread crashing issue, reenable tests.

GoogleDataTransport/GDTCORLibrary/GDTCORPlatform.m

@@ -37,6 +37,15 @@ BOOL GDTCORReachabilityFlagsContainWWAN(SCNetworkReachabilityFlags flags) {
 #endif  // TARGET_OS_IOS
 }
 
+@interface GDTCORApplication ()
+/**
+ Private flag to match the existing `readonly` public flag. This will be accurate for all platforms,
+ since we handle each platform's lifecycle notifications separately.
+ */
+@property(atomic, readwrite) BOOL isRunningInBackground;
+
+@end
+
 @implementation GDTCORApplication
 
 + (void)load {
@@ -61,6 +70,9 @@ + (nullable GDTCORApplication *)sharedApplication {
 - (instancetype)init {
   self = [super init];
   if (self) {
+    // This class will be instantiated in the foreground.
+    _isRunningInBackground = NO;
+
 #if TARGET_OS_IOS || TARGET_OS_TV
     NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter];
     [notificationCenter addObserver:self
@@ -125,16 +137,6 @@ - (BOOL)isAppExtension {
 #endif
 }
 
-- (BOOL)isRunningInBackground {
-#if TARGET_OS_IOS || TARGET_OS_TV
-  BOOL runningInBackground =
-      [[self sharedApplicationForBackgroundTask] applicationState] == UIApplicationStateBackground;
-  return runningInBackground;
-#else  // For macoS and Catalyst apps.
-  return NO;
-#endif
-}
-
 /** Returns a UIApplication instance if on the appropriate platform.
  *
  * @return The shared UIApplication if on the appropriate platform.
@@ -160,11 +162,15 @@ - (nullable id)sharedApplicationForBackgroundTask {
 
 #if TARGET_OS_IOS || TARGET_OS_TV
 - (void)iOSApplicationDidEnterBackground:(NSNotification *)notif {
+  _isRunningInBackground = YES;
+
   NSNotificationCenter *notifCenter = [NSNotificationCenter defaultCenter];
   [notifCenter postNotificationName:kGDTCORApplicationDidEnterBackgroundNotification object:nil];
 }
 
 - (void)iOSApplicationWillEnterForeground:(NSNotification *)notif {
+  _isRunningInBackground = NO;
+
   NSNotificationCenter *notifCenter = [NSNotificationCenter defaultCenter];
   [notifCenter postNotificationName:kGDTCORApplicationWillEnterForegroundNotification object:nil];
 }

GoogleDataTransport/GDTCORLibrary/Public/GDTCORPlatform.h

@@ -61,18 +61,15 @@ FOUNDATION_EXPORT const GDTCORBackgroundIdentifier GDTCORBackgroundIdentifierInv
 /** A cross-platform application class. */
 @interface GDTCORApplication : NSObject <GDTCORApplicationDelegate>
 
+/** Flag to determine if the application is running in the background. */
+@property(atomic, readonly) BOOL isRunningInBackground;
+
 /** Creates and/or returns the shared application instance.
  *
  * @return The shared application instance.
  */
 + (nullable GDTCORApplication *)sharedApplication;
 
-/** Flag to determine if the application is running in the background.
- *
- * @return YES if the app is running in the background, otherwise NO.
- */
-- (BOOL)isRunningInBackground;
-
 /** Creates a background task with the returned identifier if on a suitable platform.
  *
  * @name name The name of the task, useful for debugging which background tasks are running.

GoogleDataTransport/GDTCORTests/Lifecycle/GDTCORLifecycleTest.m

@@ -90,8 +90,11 @@ - (void)setUp {
   [[GDTCORUploadCoordinator sharedInstance] reset];
 }
 
+// Backgrounding and foregrounding are only applicable for iOS and tvOS.
+#if TARGET_OS_IOS || TARGET_OS_TV
+
 /** Tests that the library serializes itself to disk when the app backgrounds. */
-- (void)DISABLED_testBackgrounding {
+- (void)testBackgrounding {
   GDTCORTransport *transport = [[GDTCORTransport alloc] initWithMappingID:@"test"
                                                              transformers:nil
                                                                    target:kGDTCORTargetTest];
@@ -105,10 +108,8 @@ - (void)DISABLED_testBackgrounding {
       },
       5.0);
 
-  // TODO(#3973): This notification no longer triggers the `isRunningInBackground` flag. Find
-  // another way to test it.
   NSNotificationCenter *notifCenter = [NSNotificationCenter defaultCenter];
-  [notifCenter postNotificationName:kGDTCORApplicationDidEnterBackgroundNotification object:nil];
+  [notifCenter postNotificationName:UIApplicationDidEnterBackgroundNotification object:nil];
   XCTAssertTrue([GDTCORApplication sharedApplication].isRunningInBackground);
 
   GDTCORWaitForBlock(
@@ -120,7 +121,7 @@ - (void)DISABLED_testBackgrounding {
 }
 
 /** Tests that the library deserializes itself from disk when the app foregrounds. */
-- (void)DISABLED_testForegrounding {
+- (void)testForegrounding {
   GDTCORTransport *transport = [[GDTCORTransport alloc] initWithMappingID:@"test"
                                                              transformers:nil
                                                                    target:kGDTCORTargetTest];
@@ -134,10 +135,8 @@ - (void)DISABLED_testForegrounding {
       },
       5.0);
 
-  // TODO(#3973): This notification no longer triggers the `isRunningInBackground` flag. Find
-  // another way to test it.
   NSNotificationCenter *notifCenter = [NSNotificationCenter defaultCenter];
-  [notifCenter postNotificationName:kGDTCORApplicationDidEnterBackgroundNotification object:nil];
+  [notifCenter postNotificationName:UIApplicationDidEnterBackgroundNotification object:nil];
 
   GDTCORWaitForBlock(
       ^BOOL {
@@ -146,17 +145,16 @@ - (void)DISABLED_testForegrounding {
       },
       5.0);
 
-  // TODO(#3973): This notification no longer triggers the `isRunningInBackground` flag. Find
-  // another way to test it.
   [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:1.0]];
-  [notifCenter postNotificationName:kGDTCORApplicationWillEnterForegroundNotification object:nil];
+  [notifCenter postNotificationName:UIApplicationWillEnterForegroundNotification object:nil];
   XCTAssertFalse([GDTCORApplication sharedApplication].isRunningInBackground);
   GDTCORWaitForBlock(
       ^BOOL {
         return [GDTCORStorage sharedInstance].storedEvents.count > 0;
       },
       5.0);
 }
+#endif  // #if TARGET_OS_IOS || TARGET_OS_TV
 
 /** Tests that the library gracefully stops doing stuff when terminating. */
 - (void)testTermination {

GoogleDataTransportCCTSupport/GDTCCTTests/Integration/GDTCCTIntegrationTest.m

@@ -157,7 +157,11 @@ - (void)testRunsWithoutCrashing {
                 }
 
                 eventsSent += eventsUploaded.integerValue;
-                if (eventsSent == self.totalEventsGenerated) {
+                NSLog(@"Single upload event of %ld, combined for %ld/%ld total expected.",
+                      (long)eventsUploaded.integerValue, (long)eventsSent,
+                      (long)self.totalEventsGenerated);
+                // Only fulfill the expectation once event generation is done and the numbers match.
+                if (self.generateEvents == NO && eventsSent == self.totalEventsGenerated) {
                   [eventCountsMatchExpectation fulfill];
                 }
               }];