Move audioPlayer duck test

ts/test-both/state/ducks/audioPlayer_test.ts

@@ -0,0 +1,25 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+
+import { actions } from '../../../state/ducks/audioPlayer';
+import { noopAction } from '../../../state/ducks/noop';
+
+import { StateType, reducer as rootReducer } from '../../../state/reducer';
+
+describe('both/state/ducks/audioPlayer', () => {
+  const getEmptyRootState = (): StateType => {
+    return rootReducer(undefined, noopAction());
+  };
+
+  describe('setActiveAudioID', () => {
+    it("updates `activeAudioID` in the audioPlayer's state", () => {
+      const state = getEmptyRootState();
+      assert.strictEqual(state.audioPlayer.activeAudioID, undefined);
+
+      const updated = rootReducer(state, actions.setActiveAudioID('test'));
+      assert.strictEqual(updated.audioPlayer.activeAudioID, 'test');
+    });
+  });
+});