def testOneofDefaultValues(self, message_module):
    m = message_module.TestAllTypes()
    self.assertIs(None, m.WhichOneof('oneof_field'))
    self.assertFalse(m.HasField('oneof_field'))
    self.assertFalse(m.HasField('oneof_uint32'))

    # Oneof is set even when setting it to a default value.
    m.oneof_uint32 = 0
    self.assertEqual('oneof_uint32', m.WhichOneof('oneof_field'))
    self.assertTrue(m.HasField('oneof_field'))
    self.assertTrue(m.HasField('oneof_uint32'))
    self.assertFalse(m.HasField('oneof_string'))

    m.oneof_string = ""
    self.assertEqual('oneof_string', m.WhichOneof('oneof_field'))
    self.assertTrue(m.HasField('oneof_string'))
    self.assertFalse(m.HasField('oneof_uint32'))