Add isExpanded() method to Tree and TreeGrid

Fixes #9595

server/src/main/java/com/vaadin/ui/Tree.java

         treeGrid.collapse(items);
     }
 
+    /**
+     * Returns whether a given item is expanded or collapsed.
+     *
+     * @param item
+     *            the item to check
+     * @return true if the item is expanded, false if collapsed
+     */
+    public boolean isExpanded(T item) {
+        return treeGrid.isExpanded(item);
+    }
+
     /**
      * This method is a shorthand that delegates to the currently set selection
      * model.
     /**
      * Sets the height of a row. If -1 (default), the row height is calculated
      * based on the theme for an empty row before the Tree is displayed.
-     * 
+     *
      * @param rowHeight
      *            The height of a row in pixels or -1 for automatic calculation
      */
 
     /**
      * Sets the content mode of the item caption.
-     * 
+     *
      * @param contentMode
      *            the content mode
      */

server/src/main/java/com/vaadin/ui/TreeGrid.java

 import com.vaadin.ui.declarative.DesignAttributeHandler;
 import com.vaadin.ui.declarative.DesignContext;
 import com.vaadin.ui.declarative.DesignFormatter;
-import com.vaadin.ui.renderers.AbstractRenderer;
-import com.vaadin.ui.renderers.Renderer;
 
 /**
  * A grid component for displaying hierarchical tabular data.
         });
     }
 
+    /**
+     * Returns whether a given item is expanded or collapsed.
+     *
+     * @param item
+     *            the item to check
+     * @return true if the item is expanded, false if collapsed
+     */
+    public boolean isExpanded(T item) {
+        return getDataCommunicator().isExpanded(item);
+    }
+
     @Override
     protected TreeGridState getState() {
         return (TreeGridState) super.getState();

server/src/test/java/com/vaadin/tests/components/TreeTest.java

         treeData.addItem(null, "Foo");
         treeData.addItem("Foo", "Bar");
         treeData.addItem("Foo", "Baz");
-        tree.setDataProvider(
-                new TreeDataProvider<>(treeData));
+        tree.setDataProvider(new TreeDataProvider<>(treeData));
 
         TreeCollapseExpandListener listener = new TreeCollapseExpandListener(
                 tree);
 
         Assert.assertFalse(listener.isExpanded());
         tree.expand("Foo");
+        Assert.assertTrue("Item not expanded", tree.isExpanded("Foo"));
         Assert.assertTrue("Expand event not fired", listener.isExpanded());
         Assert.assertFalse(listener.isCollapsed());
         tree.collapse("Foo");
+        Assert.assertFalse("Item not collapsed", tree.isExpanded("Foo"));
         Assert.assertTrue("Collapse event not fired", listener.isCollapsed());
     }
 

server/src/test/java/com/vaadin/tests/components/treegrid/TreeGridTest.java

         // Test expand event
         Assert.assertFalse(expandEventFired);
         treeGrid.expand("Foo");
+        Assert.assertTrue("Item not expanded", treeGrid.isExpanded("Foo"));
         Assert.assertTrue("Expand event not fired", expandEventFired);
 
         // Test collapse event
         Assert.assertFalse(collapseEventFired);
         treeGrid.collapse("Foo");
+        Assert.assertFalse("Item not collapsed", treeGrid.isExpanded("Foo"));
         Assert.assertTrue("Collapse event not fired", collapseEventFired);
     }
 }