add test for disabling check button while clicking save

common/lib/xmodule/xmodule/js/spec/capa/display_spec.coffee

@@ -538,6 +538,19 @@ describe 'Problem', ->
       runs ->
         expect(window.SR.readElts).toHaveBeenCalled()
 
+    it 'disables check button while posting', ->
+      runs ->
+        spyOn($, 'postWithPrefix').andCallFake (url, answers, callback) -> callback(success: 'OK')
+        spyOn @problem, 'enableCheckButton'
+        @problem.save()
+        expect(@problem.enableCheckButton).toHaveBeenCalledWith false
+      waitsFor (->
+        return jQuery.active == 0
+      ), "jQuery requests finished", 1000
+
+      runs ->
+        expect(@problem.enableCheckButton).toHaveBeenCalledWith true
+
   describe 'refreshMath', ->
     beforeEach ->
       @problem = new Problem($('.xblock-student_view'))