add additional testing for #832, fixes function declaration

jspsych.js

@@ -1127,6 +1127,12 @@ jsPsych.plugins = (function() {
       pretty_name: 'Post trial gap',
       default: null,
       description: 'Length of gap between the end of this trial and the start of the next trial'
+    },
+    css_classes: {
+      type: module.parameterType.STRING,
+      pretty_name: 'Custom CSS classes',
+      default: null,
+      description: 'A list of CSS classes to add to the jsPsych display element for the duration of this trial'
     }
   }
 

tests/jsPsych/css-classes-parameter.test.js

@@ -35,4 +35,38 @@ describe('The css_classes parameter for trials', function(){
     expect(jsPsych.getDisplayElement().classList.contains('foo')).toBe(false);
 
   })
+
+  test('Class inherits in nested timelines', function(){
+    var tm = {
+      timeline: [{
+        type: 'html-keyboard-response',
+        stimulus: '<p>foo</p>',
+      }],
+      css_classes: ['foo']
+    }
+
+    jsPsych.init({timeline:[tm]});
+    
+    expect(jsPsych.getDisplayElement().classList.contains('foo')).toBe(true);
+    utils.pressKey(32);
+    expect(jsPsych.getDisplayElement().classList.contains('foo')).toBe(false);
+
+  })
+
+  test('Parameter works when defined as a function', function(){
+    var trial = {
+      type: 'html-keyboard-response',
+      stimulus: '<p>foo</p>',
+      css_classes: function(){ 
+        return ['foo']
+      }
+    }
+
+    jsPsych.init({timeline:[trial]});
+    
+    expect(jsPsych.getDisplayElement().classList.contains('foo')).toBe(true);
+    utils.pressKey(32);
+    expect(jsPsych.getDisplayElement().classList.contains('foo')).toBe(false);
+
+  })
 })