Add the missing expectations fullfil.

Author: visumickey

FirebasePerformance/Tests/Unit/Timer/FIRTraceTest.m

@@ -475,16 +475,17 @@ - (void)testBackgroundStateAfterTraceStop {
                                  object:[UIApplication sharedApplication]];
     [defaultCenter postNotificationName:UIApplicationDidBecomeActiveNotification
                                  object:[UIApplication sharedApplication]];
+    [expectation fulfill];
   });
 
   [self waitForExpectationsWithTimeout:5.0
                                handler:^(NSError *_Nullable error) {
                                  if (error) {
                                    XCTFail(@"Expectation failed with error: %@", error);
                                  } else {
+                                   [trace stop];
                                    XCTAssertEqual(trace.backgroundTraceState,
                                                   FPRTraceStateBackgroundAndForeground);
-                                   [trace stop];
                                  }
                                }];
 }