diff --git a/java-strings-2/src/test/java/com/baeldung/string/changecase/ToLowerCaseUnitTest.java b/java-strings-2/src/test/java/com/baeldung/string/changecase/ToLowerCaseUnitTest.java
new file mode 100644
index 0000000000..c395b61068
--- /dev/null
+++ b/java-strings-2/src/test/java/com/baeldung/string/changecase/ToLowerCaseUnitTest.java
@@ -0,0 +1,29 @@
+package com.baeldung.string.changecase;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Locale;
+
+import org.junit.Test;
+
+public class ToLowerCaseUnitTest {
+
+    private static final Locale TURKISH = new Locale("tr");
+    private String name = "John Doe";
+    private String foreignUppercase = "\u0049";
+
+    @Test
+    public void givenMixedCaseString_WhenToLowerCase_ThenResultIsLowerCase() {
+        assertEquals("john doe", name.toLowerCase());
+    }
+
+    @Test
+    public void givenForeignString_WhenToLowerCaseWithoutLocale_ThenResultIsLowerCase() {
+        assertEquals("\u0069", foreignUppercase.toLowerCase());
+    }
+
+    @Test
+    public void givenForeignString_WhenToLowerCaseWithLocale_ThenResultIsLowerCase() {
+        assertEquals("\u0131", foreignUppercase.toLowerCase(TURKISH));
+    }
+}
diff --git a/java-strings-2/src/test/java/com/baeldung/string/changecase/ToUpperCaseUnitTest.java b/java-strings-2/src/test/java/com/baeldung/string/changecase/ToUpperCaseUnitTest.java
new file mode 100644
index 0000000000..1807f854b2
--- /dev/null
+++ b/java-strings-2/src/test/java/com/baeldung/string/changecase/ToUpperCaseUnitTest.java
@@ -0,0 +1,29 @@
+package com.baeldung.string.changecase;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Locale;
+
+import org.junit.Test;
+
+public class ToUpperCaseUnitTest {
+
+    private static final Locale TURKISH = new Locale("tr");
+    private String name = "John Doe";
+    private String foreignLowercase = "\u0069";
+
+    @Test
+    public void givenMixedCaseString_WhenToUpperCase_ThenResultIsUpperCase() {
+        assertEquals("JOHN DOE", name.toUpperCase());
+    }
+
+    @Test
+    public void givenForeignString_WhenToUpperCaseWithoutLocale_ThenResultIsUpperCase() {
+        assertEquals("\u0049", foreignLowercase.toUpperCase());
+    }
+
+    @Test
+    public void givenForeignString_WhenToUpperCaseWithLocale_ThenResultIsUpperCase() {
+        assertEquals("\u0130", foreignLowercase.toUpperCase(TURKISH));
+    }
+}