KTLN-693: How to Reverse a Sentence in Kotlin (#656)

* Added unit tests

* unit tests fixes

Author: nappy29

core-kotlin-modules/core-kotlin-strings-3/src/test/kotlin/com/baeldung/reversesentence/ReverseSentenceUnitTest.kt

@@ -0,0 +1,48 @@
+package com.baeldung.reversesentence
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class ReverseSentenceUnitTest {
+    @Test
+    fun `reverse sentence using custom method`() {
+        val sentence = "this is a sentence"
+        val expected = "ecnetnes a si siht"
+        assertEquals(expected, reverseSentence(sentence))
+    }
+
+    @Test
+    fun `reverse sentence using string reversed() method`() {
+        val sentence = "this is a sentence"
+        val expected = "ecnetnes a si siht"
+        assertEquals(expected, sentence.reversed())
+    }
+
+    @Test
+    fun `reverse sentence using stringbuilder reverse() method`() {
+        val sentence = "this is a sentence"
+        val expected = "ecnetnes a si siht"
+        assertEquals(expected, StringBuilder(sentence).reverse().toString())
+    }
+
+    @Test
+    fun `reverse sentence using recursion method`() {
+        val sentence = "this is a sentence"
+        val expected = "ecnetnes a si siht"
+        assertEquals(expected, reverseSentenceRecursively(sentence))
+    }
+
+}
+fun reverseSentence(sentence: String): String {
+    var reversedSentence = ""
+    for (i in sentence.length - 1 downTo 0) {
+        reversedSentence += sentence[i]
+    }
+    return reversedSentence
+}
+fun reverseSentenceRecursively(sentence: String): String {
+    return if (sentence.isEmpty()) {
+        ""
+    } else {
+        reverseSentenceRecursively(sentence.substring(1)) + sentence[0]
+    }
+}