Re-render forum responses when marked as answer

common/static/coffee/spec/discussion/discussion_spec_helper.coffee

@@ -3,4 +3,4 @@ class @DiscussionSpecHelper
     @setUpGlobals = ->
         DiscussionUtil.loadRoles({"Moderator": [], "Administrator": [], "Community TA": []})
         window.$$course_id = "edX/999/test"
-        window.user = new DiscussionUser({id: "567", upvoted_ids: []})
+        window.user = new DiscussionUser({username: "test_user", id: "567", upvoted_ids: []})

common/static/coffee/spec/discussion/view/thread_response_show_view_spec.coffee

@@ -97,3 +97,14 @@ describe "ThreadResponseShowView", ->
         @view.render()
         expect(@view.$(".posted-details").text()).toMatch("marked as answer less than a minute ago")
         expect(@view.$(".posted-details").text()).not.toMatch(" by ")
+
+    it "re-renders correctly when endorsement changes", ->
+        @thread.set("thread_type", "question")
+        @comment.updateInfo({"ability": {"can_endorse": true}})
+        expect(@view.$(".posted-details").text()).not.toMatch("marked as answer")
+        @view.$(".action-endorse").click()
+        expect(@view.$(".posted-details").text()).toMatch(
+          "marked as answer less than a minute ago by " + user.get("username")
+        )
+        @view.$(".action-endorse").click()
+        expect(@view.$(".posted-details").text()).not.toMatch("marked as answer")

common/static/coffee/src/discussion/views/thread_response_show_view.coffee

@@ -17,7 +17,7 @@ if Backbone?
 
     initialize: ->
         super()
-        @model.on "change", @updateModelDetails
+        @listenTo(@model, "change", @render)
 
     renderTemplate: ->
         @template = _.template($("#thread-response-show-template").html())
@@ -60,8 +60,16 @@ if Backbone?
       $elem = $(event.target)
       url = @model.urlFor('endorse')
       endorsed = @model.get('endorsed')
-      data = { endorsed: not endorsed }
-      @model.set('endorsed', not endorsed)
+      new_endorsed = not endorsed
+      data = { endorsed: new_endorsed }
+      endorsement = {
+        "username": window.user.get("username"),
+        "time": new Date().toISOString()
+      }
+      @model.set(
+        "endorsed": new_endorsed
+        "endorsement": if new_endorsed then endorsement else null
+      )
       @trigger "comment:endorse", not endorsed
       DiscussionUtil.safeAjax
         $elem: $elem
@@ -86,7 +94,3 @@ if Backbone?
         @$("[data-role=thread-flag]").addClass("notflagged")      
         @$(".discussion-flag-abuse").attr("aria-pressed", "false")
         @$(".discussion-flag-abuse .flag-label").html(gettext("Report Misuse"))
-        
-    updateModelDetails: =>
-      @renderVote()
-      @renderFlagged()