diff --git a/tests/test_string.cpp b/tests/test_string.cpp
index b6ff972e..79b32c3a 100644
--- a/tests/test_string.cpp
+++ b/tests/test_string.cpp
@@ -41,6 +41,7 @@ class TestString : public CppUnit::TestFixture
   CPPUNIT_TEST(testAppendCharDetach);
   CPPUNIT_TEST(testAppendStringDetach);
   CPPUNIT_TEST(testToInt);
+  CPPUNIT_TEST(testSubstr);
   CPPUNIT_TEST_SUITE_END();
 
 public:
@@ -193,6 +194,13 @@ public:
     CPPUNIT_ASSERT_EQUAL(String("-123aa").toInt(), -123);
   }
 
+  void testSubstr()
+  {
+    CPPUNIT_ASSERT_EQUAL(String("01"), String("0123456").substr(0, 2));
+    CPPUNIT_ASSERT_EQUAL(String("12"), String("0123456").substr(1, 2));
+    CPPUNIT_ASSERT_EQUAL(String("123456"), String("0123456").substr(1, 200));
+  }
+
 };
 
 CPPUNIT_TEST_SUITE_REGISTRATION(TestString);