[tlinh2110@gmail.com] BAEL1377 - Recursion in Java (#3130)

* [tlinh2110@gmail.com] BAEL1377 - Recursion in Java

* [BAEL1377] Remove unused method

* [tlinh2110@gmail.com] Add sum method

* [tlinh2110@gmail.com] Add example for iterative approach

core-java/src/test/java/com/baeldung/recursion/RecursionExampleTest.java

@@ -0,0 +1,61 @@
+package com.baeldung.recursion;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class RecursionExampleTest {
+    
+    RecursionExample recursion = new RecursionExample();
+
+    @Test
+    public void testPowerOf10() {
+        int p0 = recursion.powerOf10(0);
+        int p1 = recursion.powerOf10(1);
+        int p4 = recursion.powerOf10(4);
+        
+        Assert.assertEquals(1, p0);
+        Assert.assertEquals(10, p1);
+        Assert.assertEquals(10000, p4);
+    }
+    
+    @Test
+    public void testFibonacci() {
+        int n0 = recursion.fibonacci(0);
+        int n1 = recursion.fibonacci(1);
+        int n7 = recursion.fibonacci(7);
+        
+        Assert.assertEquals(0, n0);
+        Assert.assertEquals(1, n1);
+        Assert.assertEquals(13, n7);
+    }
+    
+    @Test
+    public void testToBinary() {
+        String b0 = recursion.toBinary(0);
+        String b1 = recursion.toBinary(1);
+        String b10 = recursion.toBinary(10);
+        
+        Assert.assertEquals("0", b0);
+        Assert.assertEquals("1", b1);
+        Assert.assertEquals("1010", b10);
+    }
+    
+    @Test
+    public void testCalculateTreeHeight() {
+        BinaryNode root = new BinaryNode(1);
+        root.setLeft(new BinaryNode(1));
+        root.setRight(new BinaryNode(1));
+        
+        root.getLeft().setLeft(new BinaryNode(1));
+        root.getLeft().getLeft().setRight(new BinaryNode(1));
+        root.getLeft().getLeft().getRight().setLeft(new BinaryNode(1));
+        
+        root.getRight().setLeft(new BinaryNode(1));
+        root.getRight().getLeft().setRight(new BinaryNode(1));
+        
+        int height = recursion.calculateTreeHeight(root);
+        
+        Assert.assertEquals(4, height);
+    }
+
+}