Add tests for merge sort (#3715)

src/main/java/com/thealgorithms/strings/ReverseStringRecursive.java

@@ -0,0 +1,20 @@
+package com.thealgorithms.strings;
+
+/**
+ * Reverse String using Recursion
+ */
+
+public class ReverseStringRecursive {
+    /**
+     * @param str string to be reversed
+     * @return reversed string
+     */
+    public static String reverse(String str)
+    {
+        if(str.isEmpty()){
+            return str;
+        } else {
+            return reverse(str.substring(1))+str.charAt(0);
+        }
+    }
+}