chore(tests): Adds attribute passthrough test helper

function propagateAttributes can be used in testing that simple
componenets passthrough className, id, style, or other attrs

[#87784030]

spec/pivotal-ui-react/spec_helper.js

@@ -36,6 +36,20 @@ class TransitionGroupMock extends global.React.Component {
   };
 }
 
+export function propagateAttributes(componentIdentifier, attributeHash) {
+  describe('when className, id and style are given', () => {
+    it('adds className to the correct component', () => {
+      expect(componentIdentifier).toHaveClass(attributeHash.className);
+    });
+    it('adds id to the correct component', () => {
+      expect(componentIdentifier).toHaveAttr('id', attributeHash.id);
+    });
+    it('adds style to the correct component', () => {
+      expect(componentIdentifier).toHaveCss(attributeHash.style);
+    });
+  });
+}
+
 beforeEach(function() {
   jasmine.clock().install();
   $('body').find('#root').remove().end().append('<main id="root"/>');