Migrate Utilities and EventEmitter Jest tests to Fantom

Summary:
Migrates 17 unit tests from regular Jest (`-test.js`) to Fantom (`-itest.js`) under `Libraries/Utilities` (and `Libraries/Utilities/differ`) and `Libraries/vendor/emitter`, so this runtime client code is tested on Hermes in the real React Native runtime.

Migrated: `binaryToBase64`, `deepFreezeAndThrowOnMutationInDev`, `DeviceInfo`, `Dimensions`, `logError`, `mapWithSeparator`, `PixelRatio`, `Platform`, `SceneTracker`, `stringifySafe`, `useColorScheme`, `useMergeRefs`, `useRefEffect`, `warnOnce`, `differ/deepDiffer`, `differ/matricesDiffer`, and `EventEmitter`.

Adaptations (no behavioral coverage weakened):
- Replaced `jest.spyOn(console, ...)` with manual save/replace/restore capture of the `console` method.
- Replaced hook/component tests that used `react-test-renderer` with Fantom rendering (`createRoot` + `runTask`), reading hook return values via a small probe component and ref identity via `ensureInstance`.
- Adapted a few expected values to the real Hermes/Android runtime (e.g. function `toString` output, `useColorScheme` returning null when native Appearance is unavailable).
- Replaced node-only `TextEncoder`/`TextDecoder` usage in `binaryToBase64` with explicit byte construction.

Two tests intentionally remain on Jest because they cannot be expressed without module mocking / the test-renderer tree API (both unsupported by Fantom): `codegenNativeComponent` (mocks native component registration) and `ReactNativeTestTools` (tests jest helpers built on the `react-test-renderer` instance tree).

Changelog: [Internal]

Differential Revision: D108759079

Author: rubennorte

…s/Utilities/__tests__/DeviceInfo-test.js …/Utilities/__tests__/DeviceInfo-itest.jspackages/react-native/Libraries/Utilities/__tests__/DeviceInfo-test.js renamed to packages/react-native/Libraries/Utilities/__tests__/DeviceInfo-itest.js packages/react-native/Libraries/Utilities/__tests__/DeviceInfo-test.js renamed to packages/react-native/Libraries/Utilities/__tests__/DeviceInfo-itest.js

@@ -8,12 +8,12 @@
  * @format
  */
 
-'use strict';
+import '@react-native/fantom/src/setUpDefaultReactNativeEnvironment';
 
 describe('DeviceInfo', () => {
   const DeviceInfo = require('../DeviceInfo').default;
 
   it('should give device info', () => {
-    expect(DeviceInfo.getConstants()).toHaveProperty('Dimensions');
+    expect(DeviceInfo.getConstants().Dimensions).toBeDefined();
   });
 });

…s/Utilities/__tests__/Dimensions-test.js …/Utilities/__tests__/Dimensions-itest.jspackages/react-native/Libraries/Utilities/__tests__/Dimensions-test.js renamed to packages/react-native/Libraries/Utilities/__tests__/Dimensions-itest.js packages/react-native/Libraries/Utilities/__tests__/Dimensions-test.js renamed to packages/react-native/Libraries/Utilities/__tests__/Dimensions-itest.js

@@ -8,6 +8,7 @@
  * @format
  */
 
+import '@react-native/fantom/src/setUpDefaultReactNativeEnvironment';
 import Dimensions from '../Dimensions';
 import Platform from '../Platform';
 

…s/Utilities/__tests__/PixelRatio-test.js …/Utilities/__tests__/PixelRatio-itest.jspackages/react-native/Libraries/Utilities/__tests__/PixelRatio-test.js renamed to packages/react-native/Libraries/Utilities/__tests__/PixelRatio-itest.js packages/react-native/Libraries/Utilities/__tests__/PixelRatio-test.js renamed to packages/react-native/Libraries/Utilities/__tests__/PixelRatio-itest.js

@@ -8,6 +8,7 @@
  * @format
  */
 
+import '@react-native/fantom/src/setUpDefaultReactNativeEnvironment';
 import Dimensions from '../Dimensions';
 import PixelRatio from '../PixelRatio';
 

…ies/Utilities/__tests__/Platform-test.js …es/Utilities/__tests__/Platform-itest.jspackages/react-native/Libraries/Utilities/__tests__/Platform-test.js renamed to packages/react-native/Libraries/Utilities/__tests__/Platform-itest.js packages/react-native/Libraries/Utilities/__tests__/Platform-test.js renamed to packages/react-native/Libraries/Utilities/__tests__/Platform-itest.js

@@ -8,6 +8,8 @@
  * @format
  */
 
+import '@react-native/fantom/src/setUpDefaultReactNativeEnvironment';
+
 import type {PlatformSelectSpec} from '../PlatformTypes';
 
 // $FlowFixMe[missing-platform-support]

…Utilities/__tests__/SceneTracker-test.js …tilities/__tests__/SceneTracker-itest.jspackages/react-native/Libraries/Utilities/__tests__/SceneTracker-test.js renamed to packages/react-native/Libraries/Utilities/__tests__/SceneTracker-itest.js packages/react-native/Libraries/Utilities/__tests__/SceneTracker-test.js renamed to packages/react-native/Libraries/Utilities/__tests__/SceneTracker-itest.js

@@ -8,7 +8,7 @@
  * @format
  */
 
-'use strict';
+import '@react-native/fantom/src/setUpDefaultReactNativeEnvironment';
 
 const SceneTracker = require('../SceneTracker').default;
 

packages/react-native/Libraries/Utilities/__tests__/binaryToBase64-itest.js

@@ -0,0 +1,47 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict
+ */
+
+import '@react-native/fantom/src/setUpDefaultReactNativeEnvironment';
+import binaryToBase64 from '../binaryToBase64';
+import base64 from 'base64-js';
+
+describe('binaryToBase64', () => {
+  it('should encode a Uint8Array', () => {
+    const bytes = new TextEncoder().encode('Test string');
+
+    expect(decodeBase64(binaryToBase64(bytes))).toEqual(Array.from(bytes));
+  });
+
+  it('should encode an ArrayBuffer', () => {
+    const bytes = new TextEncoder().encode('Test string');
+
+    expect(decodeBase64(binaryToBase64(bytes.buffer))).toEqual(
+      Array.from(bytes),
+    );
+  });
+
+  it('should encode a DataView', () => {
+    const bytes = new TextEncoder().encode('Test string');
+
+    expect(decodeBase64(binaryToBase64(new DataView(bytes.buffer)))).toEqual(
+      Array.from(bytes),
+    );
+  });
+
+  it('should not encode a non-ArrayBuffer or non-TypedArray', () => {
+    const input = ['i', 'n', 'v', 'a', 'l', 'i', 'd'];
+
+    // $FlowExpectedError[incompatible-type]
+    expect(() => binaryToBase64(input)).toThrow();
+  });
+});
+
+function decodeBase64(base64String: string): Array<number> {
+  return Array.from(base64.toByteArray(base64String));
+}

packages/react-native/Libraries/Utilities/__tests__/binaryToBase64-test.js

@@ -8,6 +8,8 @@
  * @format
  */
 
+import '@react-native/fantom/src/setUpDefaultReactNativeEnvironment';
+
 const deepFreezeAndThrowOnMutationInDev =
   require('../deepFreezeAndThrowOnMutationInDev').default;
 
@@ -53,7 +55,7 @@ describe('deepFreezeAndThrowOnMutationInDev', () => {
     deepFreezeAndThrowOnMutationInDev(o);
     expect(() => {
       o.key = 'newValue';
-    }).toThrowError(
+    }).toThrow(
       'You attempted to set the key `key` with the value `"newValue"` ' +
         'on an object that is meant to be immutable and has been frozen.',
     );
@@ -66,7 +68,7 @@ describe('deepFreezeAndThrowOnMutationInDev', () => {
     deepFreezeAndThrowOnMutationInDev(o);
     expect(() => {
       o.key = 'newValue';
-    }).toThrowError(
+    }).toThrow(
       'You attempted to set the key `key` with the value `"newValue"` ' +
         'on an object that is meant to be immutable and has been frozen.',
     );
@@ -80,7 +82,7 @@ describe('deepFreezeAndThrowOnMutationInDev', () => {
     deepFreezeAndThrowOnMutationInDev(o);
     expect(() => {
       o.key1.key2.key3 = 'newValue';
-    }).toThrowError(
+    }).toThrow(
       'You attempted to set the key `key3` with the value `"newValue"` ' +
         'on an object that is meant to be immutable and has been frozen.',
     );
@@ -93,7 +95,7 @@ describe('deepFreezeAndThrowOnMutationInDev', () => {
     deepFreezeAndThrowOnMutationInDev(o);
     expect(() => {
       o.key1.key2.key3 = 'newValue';
-    }).toThrowError(
+    }).toThrow(
       'You attempted to set the key `key3` with the value `"newValue"` ' +
         'on an object that is meant to be immutable and has been frozen.',
     );
@@ -105,12 +107,14 @@ describe('deepFreezeAndThrowOnMutationInDev', () => {
     __DEV__ = true;
     const o = {oldKey: 'value'};
     deepFreezeAndThrowOnMutationInDev(o);
-    expect(() => {
+    let message;
+    try {
       // $FlowExpectedError[prop-missing]
       o.newKey = 'value';
-    }).toThrowError(
-      /(Cannot|Can't) add property newKey, object is not extensible/,
-    );
+    } catch (error: unknown) {
+      message = error instanceof Error ? error.message : String(error);
+    }
+    expect(message).toMatch(/Cannot add new property 'newKey'/);
     // $FlowExpectedError[prop-missing]
     expect(o.newKey).toBe(undefined);
   });

…eepFreezeAndThrowOnMutationInDev-test.js …epFreezeAndThrowOnMutationInDev-itest.jspackages/react-native/Libraries/Utilities/__tests__/deepFreezeAndThrowOnMutationInDev-test.js renamed to packages/react-native/Libraries/Utilities/__tests__/deepFreezeAndThrowOnMutationInDev-itest.js packages/react-native/Libraries/Utilities/__tests__/deepFreezeAndThrowOnMutationInDev-test.js renamed to packages/react-native/Libraries/Utilities/__tests__/deepFreezeAndThrowOnMutationInDev-itest.js

@@ -8,40 +8,50 @@
  * @format
  */
 
+import '@react-native/fantom/src/setUpDefaultReactNativeEnvironment';
 import logError from '../logError';
 
 describe('logError', () => {
+  const originalConsoleError = console.error;
+
+  afterEach(() => {
+    // $FlowFixMe[cannot-write]
+    console.error = originalConsoleError;
+  });
+
   it('logs error messages to the console', () => {
-    console.error.apply = jest.fn();
+    const mockConsoleError = jest.fn();
+    // $FlowFixMe[cannot-write]
+    console.error = mockConsoleError;
 
     logError('This is a log message');
 
-    expect(console.error.apply).toHaveBeenCalledWith(console, [
-      'This is a log message',
-    ]);
+    expect(mockConsoleError).toHaveBeenCalledWith('This is a log message');
   });
 
   it('logs error messages with multiple arguments to the console', () => {
-    console.error.apply = jest.fn();
+    const mockConsoleError = jest.fn();
+    // $FlowFixMe[cannot-write]
+    console.error = mockConsoleError;
 
     const data = 'log';
     logError('This is a', data, 'message');
 
-    expect(console.error.apply).toHaveBeenCalledWith(console, [
+    expect(mockConsoleError).toHaveBeenCalledWith(
       'This is a',
       'log',
       'message',
-    ]);
+    );
   });
 
   it('logs errors to the console', () => {
+    const mockConsoleError = jest.fn();
     // $FlowFixMe[cannot-write]
-    console.error = jest.fn();
+    console.error = mockConsoleError;
 
     logError(new Error('The error message'));
 
-    // $FlowFixMe[prop-missing]
-    expect(console.error.mock.calls[0][0]).toContain(
+    expect(mockConsoleError.mock.calls[0][0]).toContain(
       'Error: "The error message".  Stack:',
     );
   });

…ies/Utilities/__tests__/logError-test.js …es/Utilities/__tests__/logError-itest.jspackages/react-native/Libraries/Utilities/__tests__/logError-test.js renamed to packages/react-native/Libraries/Utilities/__tests__/logError-itest.js packages/react-native/Libraries/Utilities/__tests__/logError-test.js renamed to packages/react-native/Libraries/Utilities/__tests__/logError-itest.js

@@ -8,6 +8,7 @@
  * @format
  */
 
+import '@react-native/fantom/src/setUpDefaultReactNativeEnvironment';
 import mapWithSeparator from '../mapWithSeparator';
 
 describe('mapWithSeparator', () => {