update elements and fix some bugs

lib/src/paper-dropdown-menu/test/paper-dropdown-menu.html

Index: lib/src/paper-dropdown-menu/test/paper-dropdown-menu.html
diff --git a/lib/src/paper-dropdown-menu/test/paper-dropdown-menu.html b/lib/src/paper-dropdown-menu/test/paper-dropdown-menu.html
index bc652582af9d3b9d53a4254b7ca47c7e836e4548..537a5154adc793ac64a60c898c9e3998d54a565d 100644
--- a/lib/src/paper-dropdown-menu/test/paper-dropdown-menu.html
+++ b/lib/src/paper-dropdown-menu/test/paper-dropdown-menu.html
@@ -119,6 +119,57 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
           expect(dropdownMenu.selectedItem).to.be.equal(secondItem);
         });
       });
+
+      suite('deselecting', function() {
+        var menu;
+
+        setup(function() {
+          dropdownMenu = fixture('PreselectedDropdownMenu');
+          menu = Polymer.dom(dropdownMenu).querySelector('.dropdown-content');
+        });
+
+        test('an `iron-deselect` event clears the current selection', function() {
+          menu.selected = null;
+          expect(dropdownMenu.selectedItem).to.be.equal(null);
+        });
+      });
+
+      suite('validation', function() {
+        test('a non required dropdown is valid regardless of its selection', function() {
+          var dropdownMenu = fixture('TrivialDropdownMenu');
+          menu = Polymer.dom(dropdownMenu).querySelector('.dropdown-content');
+
+          // no selection.
+          expect(dropdownMenu.validate()).to.be.true;
+          expect(dropdownMenu.invalid).to.be.false;
+          expect(dropdownMenu.value).to.not.be.ok;
+
+          // some selection.
+          menu.selected = 1;
+          expect(dropdownMenu.validate()).to.be.true;
+          expect(dropdownMenu.invalid).to.be.false;
+          expect(dropdownMenu.value).to.be.equal('Bar');
+        });
+
+        test('a required dropdown is invalid without a selection', function() {
+          var dropdownMenu = fixture('TrivialDropdownMenu');
+          dropdownMenu.required = true;
+
+          // no selection.
+          expect(dropdownMenu.validate()).to.be.false;
+          expect(dropdownMenu.invalid).to.be.true;
+          expect(dropdownMenu.value).to.not.be.ok;
+        });
+
+        test('a required dropdown is valid with a selection', function() {
+          var dropdownMenu = fixture('PreselectedDropdownMenu');
+          dropdownMenu.required = true;
+          
+          expect(dropdownMenu.validate()).to.be.true;
+          expect(dropdownMenu.invalid).to.be.false;
+          expect(dropdownMenu.value).to.be.equal('Bar');
+        });
+      });
     });
   </script>