fix: mentions are not rendered properly in slack (#6762)

spec/lib/integrations/slack/send_on_slack_service_spec.rb

@@ -132,5 +132,46 @@ describe Integrations::Slack::SendOnSlackService do
         expect(hook).to have_received(:authorization_error!)
       end
     end
+
+    context 'when message contains mentions' do
+      it 'sends formatted message to slack along with inbox name when identifier not present' do
+        inbox = conversation.inbox
+        message.update!(content: "Hi [@#{contact.name}](mention://user/#{contact.id}/#{contact.name}), welcome to Chatwoot!")
+        formatted_message_text = message.content.gsub(RegexHelper::MENTION_REGEX, '\1')
+
+        expect(slack_client).to receive(:chat_postMessage).with(
+          channel: hook.reference_id,
+          text: "\n*Inbox:* #{inbox.name} (#{inbox.inbox_type})\n\n#{formatted_message_text}",
+          username: "#{message.sender.name} (Contact)",
+          thread_ts: nil,
+          icon_url: anything
+        ).and_return(slack_message)
+
+        builder.perform
+      end
+
+      it 'sends formatted message to slack when identifier is present' do
+        conversation.update!(identifier: 'random_slack_thread_ts')
+        message.update!(content: "Hi [@#{contact.name}](mention://user/#{contact.id}/#{contact.name}), welcome to Chatwoot!")
+        formatted_message_text = message.content.gsub(RegexHelper::MENTION_REGEX, '\1')
+
+        expect(slack_client).to receive(:chat_postMessage).with(
+          channel: hook.reference_id,
+          text: formatted_message_text,
+          username: "#{message.sender.name} (Contact)",
+          thread_ts: 'random_slack_thread_ts',
+          icon_url: anything
+        ).and_return(slack_message)
+
+        builder.perform
+      end
+
+      it 'will not throw error if message content is nil' do
+        message.update!(content: nil)
+        conversation.update!(identifier: 'random_slack_thread_ts')
+
+        expect { builder.perform }.not_to raise_error
+      end
+    end
   end
 end