chore: Add subject to the slack message (#6404)

spec/lib/integrations/slack/send_on_slack_service_spec.rb

@@ -2,7 +2,8 @@ require 'rails_helper'
 
 describe Integrations::Slack::SendOnSlackService do
   let!(:contact) { create(:contact) }
-  let!(:conversation) { create(:conversation, contact: contact, identifier: nil) }
+  let(:channel_email) { create(:channel_email) }
+  let!(:conversation) { create(:conversation, inbox: channel_email.inbox, contact: contact, identifier: nil) }
   let(:account) { conversation.account }
   let!(:hook) { create(:integrations_hook, account: account) }
   let!(:message) do
@@ -38,6 +39,32 @@ describe Integrations::Slack::SendOnSlackService do
 
         expect(conversation.reload.identifier).to eq '12345.6789'
       end
+
+      context 'with subject line in email' do
+        let(:message) do
+          create(:message,
+                 content_attributes: { 'email': { 'subject': 'Sample subject line' } },
+                 content: 'Sample Body',
+                 account: conversation.account,
+                 inbox: conversation.inbox, conversation: conversation)
+        end
+
+        it 'creates slack message with subject line' do
+          inbox = conversation.inbox
+
+          expect(slack_client).to receive(:chat_postMessage).with(
+            channel: hook.reference_id,
+            text: "\n*Inbox:* #{inbox.name} (#{inbox.inbox_type})\n*Subject:* Sample subject line\n\n\n#{message.content}",
+            username: "#{message.sender.name} (Contact)",
+            thread_ts: nil,
+            icon_url: anything
+          ).and_return(slack_message)
+
+          builder.perform
+
+          expect(conversation.reload.identifier).to eq '12345.6789'
+        end
+      end
     end
 
     context 'with identifier' do