diff --git a/tests/test_string.cpp b/tests/test_string.cpp
index 0e2807ef..779ada67 100644
--- a/tests/test_string.cpp
+++ b/tests/test_string.cpp
@@ -43,6 +43,7 @@ class TestString : public CppUnit::TestFixture
   CPPUNIT_TEST(testToInt);
   CPPUNIT_TEST(testSubstr);
   CPPUNIT_TEST(testNewline);
+  CPPUNIT_TEST(testUpper);
   CPPUNIT_TEST_SUITE_END();
 
 public:
@@ -237,6 +238,14 @@ public:
     CPPUNIT_ASSERT_EQUAL(L'\x0d', String(crlf)[3]);
     CPPUNIT_ASSERT_EQUAL(L'\x0a', String(crlf)[4]);
   }
+  
+  void testUpper()
+  {
+    String s1 = "tagLIB 012 strING";
+    String s2 = s1.upper();
+    CPPUNIT_ASSERT_EQUAL(String("tagLIB 012 strING"), s1);
+    CPPUNIT_ASSERT_EQUAL(String("TAGLIB 012 STRING"), s2);
+  }
 
 };