Fix FirebaseCore tests comments (#13777)

FirebaseCore/Tests/Unit/FIRAppTest.m

@@ -115,7 +115,7 @@ + (void)tearDown {
   // We stop mocking `FIRHeartbeatLogger` in the class `tearDown` method to
   // prevent interfering with other tests that use the real `FIRHeartbeatLogger`.
   // Doing this in the instance `tearDown` causes test failures due to a race
-  // condition between `NSNoticationCenter` and `OCMVerifyAllWithDelay`.
+  // condition between `NSNotificationCenter` and `OCMVerifyAllWithDelay`.
   // Affected tests:
   // - testHeartbeatLogIsAttemptedWhenAppDidBecomeActive
   [OCMClassMock([FIRHeartbeatLogger class]) stopMocking];
@@ -301,7 +301,7 @@ - (void)testConfigureDefaultAppInExtension {
   XCTAssertThrows([FIRApp configureWithOptions:differentOptions]);
   XCTAssertEqual([FIRApp allApps].count, 1);
 
-  // Explicily stop the environmentMock.
+  // Explicitly stop the environmentMock.
   [environmentMock stopMocking];
   environmentMock = nil;
 }
@@ -330,7 +330,7 @@ - (void)testConfigureCustomAppInExtension {
   XCTAssertThrows([FIRApp configureWithName:kFIRTestAppName1 options:differentOptions]);
   XCTAssertEqual([FIRApp allApps].count, 1);
 
-  // Explicily stop the environmentMock.
+  // Explicitly stop the environmentMock.
   [environmentMock stopMocking];
   environmentMock = nil;
 }
@@ -601,7 +601,7 @@ - (void)testAppIDContainsInvalidBundleIDHash {
 // Uncomment if you need to measure performance of [FIRApp validateAppID:].
 // It is commented because measures are heavily dependent on a build agent configuration,
 // so it cannot produce reliable resault on CI
-//- (void)testAppIDValidationPerfomance {
+//- (void)testAppIDValidationPerformance {
 //  [self measureBlock:^{
 //    for (NSInteger i = 0; i < 100; ++i) {
 //      [self testAppIDPrefix];