restore BaseSingletonDOMElementFactoryTest.checkFlush test

kie-wb-common-dmn/kie-wb-common-dmn-client/src/test/java/org/kie/workbench/common/dmn/client/widgets/grid/columns/factory/BaseSingletonDOMElementFactoryTest.java

@@ -125,7 +125,7 @@ public void checkAttachDomElement() {
                      domElementOnDisplay);
     }
 
-    //@Test
+    @Test
     @SuppressWarnings("unchecked")
     public void checkFlush() {
         final F factory = getFactoryForFlushTest();