fix: set default content type as text for message (#3060)

Fixes #2974

spec/controllers/api/v1/accounts/conversations/messages_controller_spec.rb

@@ -35,7 +35,7 @@ RSpec.describe 'Conversation Messages API', type: :request do
         expect(conversation.messages.first.content).to eq(params[:content])
       end
 
-      it 'creates an outgoing message with a specific bot sender' do
+      it 'creates an outgoing text message with a specific bot sender' do
         agent_bot = create(:agent_bot)
         time_stamp = Time.now.utc.to_s
         params = { content: 'test-message', external_created_at: time_stamp, sender_type: 'AgentBot', sender_id: agent_bot.id }
@@ -50,6 +50,7 @@ RSpec.describe 'Conversation Messages API', type: :request do
         expect(response_data['content_attributes']['external_created_at']).to eq time_stamp
         expect(conversation.messages.count).to eq(1)
         expect(conversation.messages.last.sender_id).to eq(agent_bot.id)
+        expect(conversation.messages.last.content_type).to eq('text')
       end
 
       it 'creates a new outgoing message with attachment' do

spec/models/message_spec.rb

@@ -77,4 +77,13 @@ RSpec.describe Message, type: :model do
       expect(ConversationReplyEmailWorker).not_to have_received(:perform_in)
     end
   end
+
+  context 'when content_type is blank' do
+    let(:message) { build(:message, content_type: nil, account: create(:account)) }
+
+    it 'sets content_type as text' do
+      message.save!
+      expect(message.content_type).to eq 'text'
+    end
+  end
 end