diff --git a/core-kotlin/src/main/kotlin/com/baeldung/kotlin/ListUtil.kt b/core-kotlin/src/main/kotlin/com/baeldung/kotlin/ListUtil.kt
deleted file mode 100644
index 0a48a42e13..0000000000
--- a/core-kotlin/src/main/kotlin/com/baeldung/kotlin/ListUtil.kt
+++ /dev/null
@@ -1,9 +0,0 @@
-@file:JvmName("Lists")
-package com.baeldung.kotlin
-
-fun <T> MutableList<T>.swap(firstIndex: Int, secondIndex: Int): MutableList<T> {
-    val tmp = this[firstIndex]
-    this[firstIndex] = this[secondIndex]
-    this[secondIndex] = tmp
-    return this
-}
diff --git a/core-kotlin/src/main/kotlin/com/baeldung/kotlin/StringUtil.kt b/core-kotlin/src/main/kotlin/com/baeldung/kotlin/StringUtil.kt
new file mode 100644
index 0000000000..ca57b2965e
--- /dev/null
+++ b/core-kotlin/src/main/kotlin/com/baeldung/kotlin/StringUtil.kt
@@ -0,0 +1,9 @@
+@file:JvmName("Strings")
+package com.baeldung.kotlin
+
+fun String.escapeForXml() : String {
+    return this
+            .replace("&", "&amp;")
+            .replace("<", "&lt;")
+            .replace(">", "&gt;")
+}
diff --git a/core-kotlin/src/test/java/com/baeldung/kotlin/ListUtilTest.java b/core-kotlin/src/test/java/com/baeldung/kotlin/ListUtilTest.java
deleted file mode 100644
index 4184cc0878..0000000000
--- a/core-kotlin/src/test/java/com/baeldung/kotlin/ListUtilTest.java
+++ /dev/null
@@ -1,22 +0,0 @@
-package com.baeldung.kotlin;
-
-import org.junit.Assert;
-import org.junit.Test;
-
-import java.util.Arrays;
-import java.util.List;
-
-import static com.baeldung.kotlin.Lists.*;
-
-public class ListUtilTest {
-
-    @Test
-    public void shouldSwapTwoElementsInList() {
-        List<Integer> list = Arrays.asList(0, 1, 2);
-
-        List<Integer> swappedElements = swap(list, 1, 2);
-
-        Assert.assertEquals(swappedElements, Arrays.asList(0, 2, 1));
-    }
-
-}
diff --git a/core-kotlin/src/test/java/com/baeldung/kotlin/StringUtilTest.java b/core-kotlin/src/test/java/com/baeldung/kotlin/StringUtilTest.java
new file mode 100644
index 0000000000..e02d3c4341
--- /dev/null
+++ b/core-kotlin/src/test/java/com/baeldung/kotlin/StringUtilTest.java
@@ -0,0 +1,30 @@
+package com.baeldung.kotlin;
+
+import kotlin.text.StringsKt;
+import org.junit.Assert;
+import org.junit.Test;
+
+import static com.baeldung.kotlin.Strings.*;
+
+
+public class StringUtilTest {
+
+    @Test
+    public void shouldSwapTwoElementsInList() {
+        String xml = "<a>hi</a>";
+
+        String escapedXml = escapeForXml(xml);
+
+        Assert.assertEquals("&lt;a&gt;hi&lt;/a&gt;", escapedXml);
+    }
+
+    @Test
+    public void callingBuiltInKotlinExtensionMethod() {
+        String name = "john";
+
+        String capitalizedName = StringsKt.capitalize(name);
+
+        Assert.assertEquals("John", capitalizedName);
+    }
+
+}
diff --git a/core-kotlin/src/test/kotlin/com/baeldung/kotlin/ExtensionMethods.kt b/core-kotlin/src/test/kotlin/com/baeldung/kotlin/ExtensionMethods.kt
index 09ce898860..44c5cd0ece 100644
--- a/core-kotlin/src/test/kotlin/com/baeldung/kotlin/ExtensionMethods.kt
+++ b/core-kotlin/src/test/kotlin/com/baeldung/kotlin/ExtensionMethods.kt
@@ -6,13 +6,6 @@ import org.junit.Test
 class ExtensionMethods {
     @Test
     fun simpleExtensionMethod() {
-        fun String.escapeForXml() : String {
-            return this
-                    .replace("&", "&amp;")
-                    .replace("<", "&lt;")
-                    .replace(">", "&gt;")
-        }
-
         Assert.assertEquals("Nothing", "Nothing".escapeForXml())
         Assert.assertEquals("&lt;Tag&gt;", "<Tag>".escapeForXml())
         Assert.assertEquals("a&amp;b", "a&b".escapeForXml())