def testFieldPresence(self):
    message = unittest_pb2.TestAllTypes()

    self.assertFalse(message.HasField("optional_int32"))
    self.assertFalse(message.HasField("optional_bool"))
    self.assertFalse(message.HasField("optional_nested_message"))

    with self.assertRaises(ValueError):
      message.HasField("field_doesnt_exist")

    with self.assertRaises(ValueError):
      message.HasField("repeated_int32")
    with self.assertRaises(ValueError):
      message.HasField("repeated_nested_message")

    self.assertEqual(0, message.optional_int32)
    self.assertEqual(False, message.optional_bool)
    self.assertEqual(0, message.optional_nested_message.bb)

    # Fields are set even when setting the values to default values.
    message.optional_int32 = 0
    message.optional_bool = False
    message.optional_nested_message.bb = 0
    self.assertTrue(message.HasField("optional_int32"))
    self.assertTrue(message.HasField("optional_bool"))
    self.assertTrue(message.HasField("optional_nested_message"))

    # Set the fields to non-default values.
    message.optional_int32 = 5
    message.optional_bool = True
    message.optional_nested_message.bb = 15

    self.assertTrue(message.HasField(u"optional_int32"))
    self.assertTrue(message.HasField("optional_bool"))
    self.assertTrue(message.HasField("optional_nested_message"))

    # Clearing the fields unsets them and resets their value to default.
    message.ClearField("optional_int32")
    message.ClearField(u"optional_bool")
    message.ClearField("optional_nested_message")

    self.assertFalse(message.HasField("optional_int32"))
    self.assertFalse(message.HasField("optional_bool"))
    self.assertFalse(message.HasField("optional_nested_message"))
    self.assertEqual(0, message.optional_int32)
    self.assertEqual(False, message.optional_bool)
    self.assertEqual(0, message.optional_nested_message.bb)