prevent multiple notifications (#10524)

* WIP - prevent multiple notifications

* merge promises to one

* update test, iterate each user

* revert changes in `groups.js` - filter duplicate notifications in `convertNotificationsToSafeJson`

test/api/v3/integration/notifications/prevent-multiple-notification.js

@@ -0,0 +1,39 @@
+import {
+  createAndPopulateGroup,
+} from '../../../../helpers/api-integration/v3';
+
+describe('Prevent multiple notifications', () => {
+  let partyLeader, partyMembers, party;
+
+  before(async () => {
+    let { group, groupLeader, members } = await createAndPopulateGroup({
+      groupDetails: {
+        type: 'party',
+        privacy: 'private',
+      },
+      members: 4,
+    });
+
+    party = group;
+    partyLeader = groupLeader;
+    partyMembers = members;
+  });
+
+  it('does not add the same notification twice', async () => {
+    const multipleChatMessages = [];
+
+    for (let i = 0; i < 4; i++) {
+      for (let memberIndex = 0; memberIndex < partyMembers.length; memberIndex++) {
+        multipleChatMessages.push(
+          partyMembers[memberIndex].post(`/groups/${party._id}/chat`, { message: `Message ${i}_${memberIndex}`}),
+        );
+      }
+    }
+
+    await Promise.all(multipleChatMessages);
+
+    const userWithNotification = await partyLeader.get('/user');
+
+    expect(userWithNotification.notifications.length).to.be.eq(1);
+  });
+});