Add missing test for exception on bad 5xxx opcode.

Author: craigthomas

test/test_chip8cpu.py

@@ -811,6 +811,12 @@ def test_misc_routines_raises_exception_on_unknown_op_codes(self):
             self.cpu.misc_routines()
         self.assertEqual("Unknown op-code: F0FF", str(context.exception))
 
+    def test_save_skip_routines_raises_exception_on_unknown_op_codes(self):
+        self.cpu.operand = 0x50FF
+        with self.assertRaises(UnknownOpCodeException) as context:
+            self.cpu.misc_routines()
+        self.assertEqual("Unknown op-code: 50FF", str(context.exception))
+
     def test_scroll_down_called(self):
         self.cpu.operand = 0x00C4
         self.cpu.clear_return()