Adjust to match in-house style

- Remove comments that explain expected behaviour
- Use respond_to instead of separate methods
- Return the updated object on update

app/controllers/messages/by_bots_controller.rb

@@ -18,13 +18,6 @@ class Messages::ByBotsController < MessagesController
     head :created, location: message_url(@message)
   end
 
-  # ensure_can_administer still applies, and can_administer? only grants access to
-  # a record the user created, so a bot key reaches that bot's own messages and no others.
-  def update
-    update_message
-    head :ok
-  end
-
   def destroy
     super
     head :no_content

app/controllers/messages_controller.rb

@@ -34,8 +34,14 @@ class MessagesController < ApplicationController
   end
 
   def update
-    update_message
-    redirect_to room_message_url(@room, @message)
+    @message.update!(message_params)
+
+    @message.broadcast_replace_to @room, :messages, target: [ @message, :presentation ], partial: "messages/presentation", attributes: { maintain_scroll: true }
+
+    respond_to do |format|
+      format.html { redirect_to room_message_url(@room, @message) }
+      format.json { render :show }
+    end
   end
 
   def destroy
@@ -48,13 +54,6 @@ class MessagesController < ApplicationController
       @message = @room.messages.find(params[:id])
     end
 
-    # Extracted so bots can reuse the update and its broadcast while answering with
-    # a status code instead of a redirect.
-    def update_message
-      @message.update!(message_params)
-      @message.broadcast_replace_to @room, :messages, target: [ @message, :presentation ], partial: "messages/presentation", attributes: { maintain_scroll: true }
-    end
-
     def ensure_can_administer
       head :forbidden unless Current.user.can_administer?(@message)
     end

app/views/messages/by_bots/show.json.jbuilder

@@ -0,0 +1 @@
+json.partial! "messages/message", message: @message

test/controllers/messages/by_bots_controller_test.rb

@@ -158,6 +158,12 @@ class Messages::ByBotsControllerTest < ActionDispatch::IntegrationTest
 
     assert_response :ok
     assert_equal "Deployed.", message.reload.plain_text_body
+
+    json = JSON.parse(response.body)
+    assert_equal message.id, json["id"]
+    assert_equal "Deployed.", json["body"]["plain_text"]
+    assert_equal users(:bender).id, json["creator"]["id"]
+    assert_equal room_message_url(@room, message), json["url"]
   end
 
   test "update with UTF-8 content" do
@@ -167,6 +173,7 @@ class Messages::ByBotsControllerTest < ActionDispatch::IntegrationTest
 
     assert_response :ok
     assert_equal "Deployed 🚀!", message.reload.plain_text_body
+    assert_equal "Deployed 🚀!", JSON.parse(response.body)["body"]["plain_text"]
   end
 
   test "update can't touch a message the bot did not create" do