Refactor subclassing of RCTEventEmitter

Summary:
This Diff remove the assert on the initializer in the EventEmitter in place of a more idiomatic check when the method is invoked.

It aims to solve an internal error and promotes best practices for the iOS platform.

## Changelog:
[iOS][Changed] Refactor RCTEventEmitter initialization

Differential Revision: D40762253

fbshipit-source-id: 7284c190611c31edc1ff5f937d824f0350334a53

React/Modules/RCTEventEmitter.m

@@ -23,17 +23,6 @@ + (NSString *)moduleName
   return @"";
 }
 
-+ (void)initialize
-{
-  [super initialize];
-  if (self != [RCTEventEmitter class]) {
-    RCTAssert(
-        RCTClassOverridesInstanceMethod(self, @selector(supportedEvents)),
-        @"You must override the `supportedEvents` method of %@",
-        self);
-  }
-}
-
 - (instancetype)initWithDisabledObservation
 {
   self = [super init];
@@ -43,6 +32,8 @@ - (instancetype)initWithDisabledObservation
 
 - (NSArray<NSString *> *)supportedEvents
 {
+  NSString *className = NSStringFromClass(self.class);
+  [NSException raise:@"supportedEvents Not Implemented" format:@"%@ must implement the supportedEvents method", className];
   return nil;
 }
 

packages/rn-tester/RNTesterUnitTests/RCTEventEmitterTests.m

@@ -0,0 +1,63 @@
+//
+//  RCTEventEmitterTests.m
+//  RNTesterUnitTests
+//
+//  Created by Riccardo Cipolleschi on 27/10/2022.
+//  Copyright © 2022 Facebook. All rights reserved.
+//
+
+#import <XCTest/XCTest.h>
+#import <React/RCTEventEmitter.h>
+
+#pragma mark - Faulty EventEmitter
+
+@interface RCTFaultyEventEmitter: RCTEventEmitter
+@end
+
+@implementation RCTFaultyEventEmitter
+@end
+
+#pragma mark - Proper EventEmitter
+
+@interface RCTProperEventEmitter: RCTEventEmitter
+@end
+
+@implementation RCTProperEventEmitter
+
+- (NSArray<NSString *> *)supportedEvents
+{
+  return @[@"myEvent"];
+}
+@end
+
+#pragma mark - Tests Code
+
+@interface RCTEventEmitterTests : XCTestCase
+
+@end
+
+@implementation RCTEventEmitterTests
+
+- (void)testEventEmitterSubclass_whenFaultySubclassInvokesSupportedEvents_raiseException {
+  RCTEventEmitter * emitter = [[RCTFaultyEventEmitter alloc] init];
+
+  // Not using XCTAssertThrows to actually assert informations on the exception
+  @try {
+    NSArray<NSString *> * events = emitter.supportedEvents;
+  } @catch (NSException *exception) {
+    XCTAssertEqualObjects(exception.name, @"supportedEvents Not Implemented");
+    XCTAssertEqualObjects(exception.reason, @"RCTFaultyEventEmitter must implement the supportedEvents method");
+  }
+
+}
+
+- (void)testEventEmitterSubclass_whenProperSubclassInvokesSupportedEvents_itreturnsTheEvents {
+  RCTEventEmitter * emitter = [[RCTProperEventEmitter alloc] init];
+
+  NSArray<NSString *> * events = emitter.supportedEvents;
+
+  XCTAssertEqualObjects(events, @[@"myEvent"]);
+}
+
+@end
+