FIX: Do not email group user with user_private_message notification (#11754)

There was an issue that occurred with this order of operations:

* An IMAP topic was created by emailing a group
* A second user was invited to the topic (not the OP and not the group)
* A user with access to the group replies to the topic
* The second user receives a user_private_message notification email because of their involvement in the topic
* The second user replies to the email via email

This new reply would then go and notify the other group PM users, except for those who emailed the group topic directly, which is handled via the group SMTP mailer. However because the new post already has an incoming email because it is parsed via the Email::Receiver via POP3 the group SMTP section of the post alerter is skipped, and the group's email address is not ignored for the user_private_message notification.

This PR fixes it so the group is not ever sent an email via the PM notification. This is important because any new emails in the group's IMAP inbox will be picked up by the Imap::Sync code and created as a new topic which is not at all desirable.

Also in this PR I split up the specs a bit more for group SMTP in the post alerter to make them easier to read and they each only test one thing.

spec/services/post_alerter_spec.rb

@@ -1261,67 +1261,77 @@ describe PostAlerter do
     end
 
     fab!(:topic) do
-      Fabricate(:private_message_topic,
+      Fabricate(
+        :private_message_topic,
         topic_allowed_groups: [
           Fabricate.build(:topic_allowed_group, group: group)
         ]
       )
     end
 
-    it "sends notifications for new posts in topic" do
-      PostAlerter.any_instance.expects(:create_notification).at_least_once
-      post = Fabricate(
+    def create_post_with_incoming
+      Fabricate(
         :post,
         topic: topic,
         incoming_email:
-          Fabricate(
-            :incoming_email,
-            topic: topic,
-            from_address: "foo@discourse.org",
-            to_addresses: group.email_username,
-            cc_addresses: "bar@discourse.org"
-          )
+        Fabricate(
+          :incoming_email,
+          topic: topic,
+          from_address: "foo@discourse.org",
+          to_addresses: group.email_username,
+          cc_addresses: "bar@discourse.org"
+        )
       )
-      staged_group_user = Fabricate(:staged, email: "discourse@example.com")
-      Fabricate(:topic_user, user: staged_group_user, topic: post.topic)
-      topic.allowed_users << staged_group_user
-      topic.save
+    end
+
+    it "does not send a group smtp email when the post already has an incoming email" do
+      post = create_post_with_incoming
 
       expect { PostAlerter.new.after_save_post(post, true) }.to change { ActionMailer::Base.deliveries.size }.by(0)
+    end
 
+    it "sends a group smtp email when the post does not have an incoming email" do
+      create_post_with_incoming
       post = Fabricate(:post, topic: topic)
       expect { PostAlerter.new.after_save_post(post, true) }.to change { ActionMailer::Base.deliveries.size }.by(1)
       email = ActionMailer::Base.deliveries.last
       expect(email.from).to include(group.email_username)
       expect(email.to).to contain_exactly("foo@discourse.org", "bar@discourse.org")
       expect(email.subject).to eq("Re: #{topic.title}")
+    end
 
-      post = Fabricate(
-        :post,
-        topic: topic,
-        incoming_email:
-          Fabricate(
-            :incoming_email,
-            topic: topic,
-            from_address: "bar@discourse.org",
-            to_addresses: group.email_username,
-            cc_addresses: "baz@discourse.org"
-          )
-      )
-      expect { PostAlerter.new.after_save_post(post, true) }.to change { ActionMailer::Base.deliveries.size }.by(0)
-
-      # we never want the group to be notified by email about these posts
-      PostAlerter.any_instance.expects(:create_notification).with(kind_of(User), Notification.types[:private_message], kind_of(Post), skip_send_email_to: ["foo@discourse.org", "bar@discourse.org", "baz@discourse.org", "discourse@example.com"]).at_least_once
-
-      post = Fabricate(:post, topic: topic.reload)
-      expect { PostAlerter.new.after_save_post(post, true) }.to change { ActionMailer::Base.deliveries.size }.by(1)
-      email = ActionMailer::Base.deliveries.last
-      expect(email.from).to eq([group.email_username])
-      expect(email.to).to contain_exactly("foo@discourse.org", "bar@discourse.org", "baz@discourse.org")
-      expect(email.subject).to eq("Re: #{topic.title}")
-
+    it "does not send group smtp emails for a whisper" do
+      create_post_with_incoming
       post = Fabricate(:post, topic: topic, post_type: Post.types[:whisper])
       expect { PostAlerter.new.after_save_post(post, true) }.to change { ActionMailer::Base.deliveries.size }.by(0)
     end
+
+    it "does not send a notification email to the group when the post does not have an incoming email" do
+      PostAlerter.any_instance.expects(:create_notification).with(kind_of(User), Notification.types[:private_message], kind_of(Post), skip_send_email_to: ["discourse@example.com"]).at_least_once
+      post = create_post_with_incoming
+      staged_group_user = Fabricate(:staged, email: "discourse@example.com")
+      Fabricate(:topic_user, user: staged_group_user, topic: post.topic)
+      topic.allowed_users << staged_group_user
+      topic.save
+      expect { PostAlerter.new.after_save_post(post, true) }.to change { ActionMailer::Base.deliveries.size }.by(0)
+    end
+
+    it "skips sending a notification email to the group and all other incoming email addresses" do
+
+      create_post_with_incoming
+      PostAlerter.any_instance.expects(:create_notification).with(kind_of(User), Notification.types[:private_message], kind_of(Post), skip_send_email_to: ["foo@discourse.org", "bar@discourse.org", "discourse@example.com"]).at_least_once
+
+      post = Fabricate(:post, topic: topic.reload)
+      staged_group_user = Fabricate(:staged, email: "discourse@example.com")
+      Fabricate(:topic_user, user: staged_group_user, topic: post.topic)
+      topic.allowed_users << staged_group_user
+      topic.save
+
+      expect { PostAlerter.new.after_save_post(post, true) }.to change { ActionMailer::Base.deliveries.size }.by(1)
+      email = ActionMailer::Base.deliveries.last
+      expect(email.from).to eq([group.email_username])
+      expect(email.to).to contain_exactly("foo@discourse.org", "bar@discourse.org")
+      expect(email.subject).to eq("Re: #{topic.title}")
+    end
   end
 end