Node: isRoot(): added

src/main/java/net/kemitix/node/Node.java

@@ -82,6 +82,13 @@ public interface Node<T> {
      */
     boolean isEmpty();
 
+    /**
+     * Returns true is the node is a root node (has no parent).
+     *
+     * @return true is parent is null
+     */
+    boolean isRoot();
+
     /**
      * Fetch the parent node.
      *

src/main/java/net/kemitix/node/NodeItem.java

@@ -113,6 +113,11 @@ class NodeItem<T> implements Node<T> {
         return data == null;
     }
 
+    @Override
+    public boolean isRoot() {
+        return parent == null;
+    }
+
     @Override
     public Optional<Node<T>> findParent() {
         return Optional.ofNullable(parent);

src/test/java/net/kemitix/node/NodeItemTest.java

@@ -930,4 +930,19 @@ public class NodeItemTest {
                      .collect(Collectors.toList())).as("sub-tree")
                                                    .containsExactlyInAnyOrder(n1, n3, n5, n7);
     }
+
+    @Test
+    public void isRootWhenRootIsTrue() {
+        assertThat(Nodes.unnamedRoot(null)
+                        .isRoot()).isTrue();
+    }
+
+    @Test
+    public void isRootWhenNotRootIsFalse() {
+        //given
+        val root = Nodes.unnamedRoot(null);
+        //then
+        assertThat(Nodes.unnamedChild(null, root)
+                        .isRoot()).isFalse();
+    }
 }