Incorporate the class Upper from string package (#1952)

src/main/java/com/string/Upper.java

@@ -0,0 +1,20 @@
+package com.string;
+
+public class Upper {
+
+    /**
+     * Converts all of the characters in this {@code String} to upper case
+     *
+     * @param s the string to convert
+     * @return the {@code String}, converted to uppercase.
+     */
+    public static String toUpperCase(String s) {
+        char[] values = s.toCharArray();
+        for (int i = 0; i < values.length; ++i) {
+            if (Character.isLetter(values[i]) && Character.isLowerCase(values[i])) {
+                values[i] = Character.toUpperCase(values[i]);
+            }
+        }
+        return new String(values);
+    }
+}

src/test/java/com/string/UpperTest.java

@@ -0,0 +1,15 @@
+package com.string;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+class UpperTest extends Upper {
+
+    @Test
+    void testUpper() {
+        Assertions.assertEquals(toUpperCase("abc"), ("abc").toUpperCase(), "The strings are equals");
+        //Assertions fail for functional reasons
+        Assertions.assertEquals(toUpperCase("abc"), "abc", "The strings are not equals");
+    }
+
+}