Added unit tests for module init

Summary: The module initialization process is complex and full of race conditions. This diff adds a set of unit tests that verify that modules setup happens in the correct order, and enforces all the various conditions for main/background init.

Reviewed By: javache

Differential Revision: D2994145

fb-gh-sync-id: 92ea84508cdeeb280ff0fb9e9b2dffa8dbc37e66
shipit-source-id: 92ea84508cdeeb280ff0fb9e9b2dffa8dbc37e66

React/Base/RCTModuleData.m

@@ -238,4 +238,9 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init);
   _methodQueue = nil;
 }
 
+- (NSString *)description
+{
+  return [NSString stringWithFormat:@"<%@: %p; name=\"%@\">", [self class], self, self.name];
+}
+
 @end