BAEL -1339 Implement a binary tree in Java (#3301)

* edge cases binary tree

* code cleanup

core-java/src/test/java/com/baeldung/tree/BinaryTreeTest.java

@@ -1,5 +1,6 @@
 package com.baeldung.tree;
 
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 
@@ -26,6 +27,26 @@ public class BinaryTreeTest {
         assertFalse(bt.containsNode(1));
     }
 
+    @Test
+    public void givenABinaryTree_WhenAddingExistingElement_ThenElementIsNotAdded() {
+
+        BinaryTree bt = createBinaryTree();
+
+        int initialSize = bt.getSize();
+
+        assertTrue(bt.containsNode(3));
+        bt.add(3);
+        assertEquals(initialSize, bt.getSize());
+    }
+
+    @Test
+    public void givenABinaryTree_WhenLookingForNonExistingElement_ThenReturnsFalse() {
+
+        BinaryTree bt = createBinaryTree();
+
+        assertFalse(bt.containsNode(99));
+    }
+
     @Test
     public void givenABinaryTree_WhenDeletingElements_ThenTreeDoesNotContainThoseElements() {
 
@@ -36,6 +57,19 @@ public class BinaryTreeTest {
         assertFalse(bt.containsNode(9));
     }
 
+    @Test
+    public void givenABinaryTree_WhenDeletingNonExistingElement_ThenTreeDoesNotDelete() {
+
+        BinaryTree bt = createBinaryTree();
+
+        int initialSize = bt.getSize();
+
+        assertFalse(bt.containsNode(99));
+        bt.delete(99);
+        assertFalse(bt.containsNode(99));
+        assertEquals(initialSize, bt.getSize());
+    }
+
     @Test
     public void givenABinaryTree_WhenTraversingInOrder_ThenPrintValues() {