Fix AccessibilityInfo.isDarkerSystemColorsEnabled unresolved promise (facebook#56019)

Summary:
This PR fixes a bug in the `AccessibilityInfo` component.  This is a follow up of the work I started with the PR I opened last week that has been already merged facebook#55920.

`AccessibilityInfo` exposes the method `isDarkerSystemColorsEnabled`. In the android branch, Promise.resolve(false) as return value was creating a new unrelated promise that never calls the resolve function provided by the promise executor constructor, so it hangs indefinitely.

This means that if a user calls this method on android without any `Platform.OS === 'ios'` guard, it will result in a unresolved promise.

I fixed the bug in the same way I fixed the one in the PR above: by aligning the implementation of `isDarkerSystemColorsEnabled` to the one of other methods (eg. `isBoldTextEnabled`).

I also added the tests to avoid regression, and additionally verify that the iOS method is doing what we are expecting (in both cases for when `NativeAccessibilityManagerIOS.getCurrentDarkerSystemColorsState` is available or not).
The mock of the Platform object has been done the same way I saw while doing another contribution in the Pressability-test (see facebook#55378 ).

## Changelog:

[GENERAL] [FIXED] - Fix AccessibilityInfo.isDarkerSystemColorsEnabled unresolved (never ending) promise

Pull Request resolved: facebook#56019

Test Plan: This fix, like the one in the previous PR, was develop using TDD. I first added a failing test to reproduce that the android branch of the `isDarkerSystemColorsEnabled` method was acting as described above (resulting in failure due to jest timeout because the promise was not returning). Then I applied the fix, and finally added also the test for the iOS counterpart.

Reviewed By: cortinico

Differential Revision: D95931847

Pulled By: vzaidman

fbshipit-source-id: 94cd088b286f1b724f0feeb20670b501a458c774

Author: chicio

packages/react-native/Libraries/Components/AccessibilityInfo/AccessibilityInfo.js

@@ -237,10 +237,10 @@ const AccessibilityInfo = {
    * The result is `true` when dark system colors is enabled and `false` otherwise.
    */
   isDarkerSystemColorsEnabled(): Promise<boolean> {
-    return new Promise((resolve, reject) => {
-      if (Platform.OS === 'android') {
-        return Promise.resolve(false);
-      } else {
+    if (Platform.OS === 'android') {
+      return Promise.resolve(false);
+    } else {
+      return new Promise((resolve, reject) => {
         if (
           NativeAccessibilityManagerIOS?.getCurrentDarkerSystemColorsState !=
           null
@@ -256,8 +256,8 @@ const AccessibilityInfo = {
             ),
           );
         }
-      }
-    });
+      });
+    }
   },
 
   /**

packages/react-native/Libraries/Components/AccessibilityInfo/__tests__/AccessibilityInfo-test.js

@@ -13,6 +13,9 @@ jest.unmock('../AccessibilityInfo');
 const mockGetCurrentPrefersCrossFadeTransitionsState = jest.fn(
   (onSuccess, onError) => onSuccess(true),
 );
+const mockGetCurrentDarkerSystemColorsState = jest.fn((onSuccess, onError) =>
+  onSuccess(true),
+);
 const mockNativeAccessibilityManagerDefault: {
   getCurrentPrefersCrossFadeTransitionsState: JestMockFn<
     [
@@ -21,9 +24,17 @@ const mockNativeAccessibilityManagerDefault: {
     ],
     void,
   > | null,
+  getCurrentDarkerSystemColorsState: JestMockFn<
+    [
+      onSuccess: (isDarkerSystemColorsEnabled: boolean) => void,
+      onError: (error: Error) => void,
+    ],
+    void,
+  > | null,
 } = {
   getCurrentPrefersCrossFadeTransitionsState:
     mockGetCurrentPrefersCrossFadeTransitionsState,
+  getCurrentDarkerSystemColorsState: mockGetCurrentDarkerSystemColorsState,
 };
 
 jest.mock('../NativeAccessibilityManager', () => ({
@@ -41,6 +52,7 @@ describe('AccessibilityInfo', () => {
   beforeEach(() => {
     originalPlatform = Platform.OS;
     mockGetCurrentPrefersCrossFadeTransitionsState.mockClear();
+    mockGetCurrentDarkerSystemColorsState.mockClear();
   });
 
   describe('prefersCrossFadeTransitions', () => {
@@ -91,9 +103,57 @@ describe('AccessibilityInfo', () => {
     });
   });
 
+  describe('isDarkerSystemColorsEnabled', () => {
+    describe('Android', () => {
+      it('should return immediately', async () => {
+        /* $FlowFixMe[incompatible-type] */
+        Platform.OS = 'android';
+
+        const isDarkerSystemColorsEnabled =
+          await AccessibilityInfo.isDarkerSystemColorsEnabled();
+
+        expect(isDarkerSystemColorsEnabled).toBe(false);
+      });
+    });
+
+    describe('iOS', () => {
+      it('should call getCurrentDarkerSystemColorsState if available', async () => {
+        /* $FlowFixMe[incompatible-type] */
+        Platform.OS = 'ios';
+
+        const isDarkerSystemColorsEnabled =
+          await AccessibilityInfo.isDarkerSystemColorsEnabled();
+
+        expect(mockGetCurrentDarkerSystemColorsState).toHaveBeenCalled();
+        expect(isDarkerSystemColorsEnabled).toBe(true);
+      });
+
+      it('should throw error if getCurrentDarkerSystemColorsState is not available', async () => {
+        /* $FlowFixMe[incompatible-type] */
+        Platform.OS = 'ios';
+
+        mockNativeAccessibilityManagerDefault.getCurrentDarkerSystemColorsState =
+          null;
+
+        const result: mixed =
+          await AccessibilityInfo.isDarkerSystemColorsEnabled().catch(e => e);
+
+        invariant(
+          result instanceof Error,
+          'Expected isDarkerSystemColorsEnabled to reject',
+        );
+        expect(result.message).toEqual(
+          'NativeAccessibilityManagerIOS.getCurrentDarkerSystemColorsState is not available',
+        );
+      });
+    });
+  });
+
   afterEach(() => {
     mockNativeAccessibilityManagerDefault.getCurrentPrefersCrossFadeTransitionsState =
       mockGetCurrentPrefersCrossFadeTransitionsState;
+    mockNativeAccessibilityManagerDefault.getCurrentDarkerSystemColorsState =
+      mockGetCurrentDarkerSystemColorsState;
     /* $FlowFixMe[incompatible-type] */
     Platform.OS = originalPlatform;
   });