BAEL-3153: Added test cases for String toLowerCase and toUpperCase

The toLowerCase and toUpperCase methods are simple enough that no new
classes are needed under the main/ directory. The included tests
exercise the changing of case for an English string using the default
locale, a foreign string using the default locale, and a foreign string
using a provided locale.

java-strings-2/README.MD

@@ -1,7 +1,7 @@
-## Relevant Articles
-
-- [Java Localization – Formatting Messages](https://www.baeldung.com/java-localization-messages-formatting)
-- [Check If a String Contains a Substring](https://www.baeldung.com/java-string-contains-substring)
-- [Removing Stopwords from a String in Java](https://www.baeldung.com/java-string-remove-stopwords)
-- [Blank and Empty Strings in Java](https://www.baeldung.com/java-blank-empty-strings)
-- [String Initialization in Java](https://www.baeldung.com/java-string-initialization)
+## Relevant Articles
+
+- [Java Localization – Formatting Messages](https://www.baeldung.com/java-localization-messages-formatting)
+- [Check If a String Contains a Substring](https://www.baeldung.com/java-string-contains-substring)
+- [Removing Stopwords from a String in Java](https://www.baeldung.com/java-string-remove-stopwords)
+- [Blank and Empty Strings in Java](https://www.baeldung.com/java-blank-empty-strings)
+- [String Initialization in Java](https://www.baeldung.com/java-string-initialization)

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));
+	}
+}

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 foreignUppercase = "\u0069";
+
+	@Test
+	public void givenMixedCaseString_WhenToUpperCase_ThenResultIsUpperCase() {
+		assertEquals("JOHN DOE", name.toUpperCase());
+	}
+	
+	@Test
+	public void givenForeignString_WhenToUpperCaseWithoutLocale_ThenResultIsUpperCase() {
+		assertEquals("\u0049", foreignUppercase.toUpperCase());
+	}
+	
+	@Test
+	public void givenForeignString_WhenToUpperCaseWithLocale_ThenResultIsUpperCase() {
+		assertEquals("\u0130", foreignUppercase.toUpperCase(TURKISH));
+	}
+}