Node.getChild(): method to get a child or throw an exception if not found

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

@@ -125,6 +125,16 @@ public interface Node<T> {
      */
     Optional<Node<T>> findChild(T child);
 
+    /**
+     * Fetches the node for the child if present.
+     *
+     * @param child the child's data to search for
+     *
+     * @return the child node if found
+     *
+     * @throws NodeException if the node is not found
+     */
+    Node<T> getChild(T child);
 
     /**
      * Checks if the node is an ancestor.

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

@@ -246,6 +246,14 @@ public class NodeItem<T> implements Node<T> {
                        .findAny();
     }
 
+    @Override
+    public Node<T> getChild(final T child) {
+        Optional<Node<T>> optional = findChild(child);
+        if (optional.isPresent())
+            return optional.get();
+        throw new NodeException("Child not found");
+    }
+
     /**
      * Checks if the node is an ancestor.
      *

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

@@ -901,4 +901,25 @@ public class NodeItemTest {
         assertThat(child.getParent()).isSameAs(node);
         assertThat(node.getChildren()).containsExactly(child);
     }
+
+    @Test
+    public void canGetChildWhenFound() {
+        //given
+        node = new NodeItem<>("data");
+        Node<String> child = new NodeItem<>("child data", "child name", node);
+        //when
+        Node<String> found = node.getChild("child data");
+        //then
+        assertThat(found).isSameAs(child);
+    }
+
+    @Test
+    public void canGetChildWhenNotFound() {
+        //given
+        exception.expect(NodeException.class);
+        exception.expectMessage("Child not found");
+        node = new NodeItem<>("data");
+        //when
+        node.getChild("child data");
+    }
 }