Fixing ComboBox failing tests. Need to properly fire open() only if the widget is attached.

Author: kevzlou7979

src/test/java/gwt/material/design/addins/client/ui/MaterialComboBoxTest.java

@@ -267,7 +267,7 @@ protected void dispatch(ClearEvent.ClearHandler eventHandler) {
             }
         });
         assertTrue(isClearEventFired[0]);
-        
+
         // Clearing Handler
         final boolean[] isClearingEventFired = {false};
         comboBox.addClearingHandler(event -> {
@@ -336,9 +336,8 @@ public void testAddItemOption() {
 
     }
 
-    //TODO: Failed Test
     public void testElements() {
-        /*MaterialComboBox<User> comboBox = getWidget();
+        MaterialComboBox<User> comboBox = getWidget();
 
         assertNotNull(comboBox.getDropdownContainerElement());
         assertEquals(JsComboBox.$(comboBox.getElement()).find(".select2 .selection .select2-selection__rendered").html(), comboBox.getDropdownContainerElement().html());
@@ -348,9 +347,11 @@ public void testElements() {
             firedOpenHandler[0] = true;
             assertNotNull(comboBox.getDropdownResultElement());
         });
-        comboBox.open();
 
-        assertTrue(firedOpenHandler[0]);*/
+        comboBox.addAttachHandler(attachEvent -> {
+            comboBox.open();
+            assertTrue(firedOpenHandler[0]);
+        });
     }
 
     public void testLanguage() {