FEATURE: first class group mentions built in

If you allow a group to be mentioned it can be mentioned with the @ symbol.

Keep in mind as a safety mechanism max_users_notified_per_group_mention is set to 100

spec/services/post_alerter_spec.rb

@@ -12,7 +12,7 @@ describe PostAlerter do
   context "unread" do
     it "does not return whispers as unread posts" do
       op = Fabricate(:post)
-      whisper = Fabricate(:post, raw: 'this is a whisper post',
+      _whisper = Fabricate(:post, raw: 'this is a whisper post',
                                  user: Fabricate(:admin),
                                  topic: op.topic,
                                  reply_to_post_number: op.post_number,
@@ -92,6 +92,26 @@ describe PostAlerter do
     end
   end
 
+  context '@group mentions' do
+
+    it 'notifies users correctly' do
+
+      group = Fabricate(:group, name: 'group', alias_level: Group::ALIAS_LEVELS[:everyone])
+      group.add(evil_trout)
+
+      expect {
+        create_post_with_alerts(raw: "Hello @group how are you?")
+      }.to change(evil_trout.notifications, :count).by(1)
+
+
+      group.update_columns(alias_level: Group::ALIAS_LEVELS[:members_mods_and_admins])
+
+      expect {
+        create_post_with_alerts(raw: "Hello @group you are not mentionable")
+      }.to change(evil_trout.notifications, :count).by(0)
+    end
+  end
+
   context '@mentions' do
 
     let(:user) { Fabricate(:user) }