Search (a bit to broad) returning potential tests using category to expose private methods of a tested class:

https://cs.chromium.org/search/?q=file:.*_unittest.mm+@interface%5C+%5Cw*%5C+%5C(+file:ios/&sq=package:chromium&type=cs

Example of incorrect code in ios/chrome/browser/installation_notifier_unittest.mm:

@interface InstallationNotifier (Testing)
- (void)setDispatcher:(id<DispatcherProtocol>)dispatcher;
- (void)resetDispatcher;
- (void)dispatchInstallationNotifierBlock;
- (void)registerForInstallationNotifications:(id)observer
                                withSelector:(SEL)notificationSelector
                                   forScheme:(NSString*)scheme
                                startPolling:(BOOL)poll;
- (net::BackoffEntry::Policy const*)backOffPolicy;
@end