FlipperClient tests on iOS

Summary:
This diff adds few tests for flipper client on iOS side. This tests are similar to the ones which exists in xplat but this tests the iOS side of flipper client.

Following tests are added

- connect , disconnect block called on plugin
- background plugin activated before init method
- crash getting suppressed

Reviewed By: jknoxville

Differential Revision: D13167637

fbshipit-source-id: 6c21d5cf2f08e7e3c17ecacbf3badfbde80fb5d1

iOS/FlipperKit/FlipperClient.mm

@@ -15,6 +15,7 @@
 #import <UIKit/UIKit.h>
 #include "SKStateUpdateCPPWrapper.h"
 #import "FlipperDiagnosticsViewController.h"
+#import "FlipperClient+Testing.h"
 
 #if !TARGET_OS_SIMULATOR
 //#import "SKPortForwardingServer.h"
@@ -177,4 +178,15 @@ using WrapperPlugin = facebook::flipper::FlipperCppWrapperPlugin;
 
 @end
 
+@implementation FlipperClient (Testing)
+
+- (instancetype)initWithCppClient:(facebook::flipper::FlipperClient *)cppClient {
+    if (self = [super init]) {
+        _cppClient = cppClient;
+    }
+    return self;
+}
+
+@end
+
 #endif