add a decrypt string test

Author: pwnipc

src/test/java/CaesarShiftTest.java

@@ -21,5 +21,11 @@ public void caesarShift_isDecryptMsgUpcasedTest_String() {
         assertEquals(true, Character.isUpperCase(caseTest.decrypt("a").charAt(0)));
     }
 
+    @Test
+    public void caesarShift_decryptStringTest_String(){
+        CaesarShift decryptStringTest = new CaesarShift();
+        assertEquals("Z", decryptStringTest.decrypt("Y"));
+    }
+
 
 }