def METHOD_NAME(self, container: MetadataContainer):
    namespace = self.gen_key()
    key = f"{fake.unique.word()}/{fake.unique.word()}"
    value = random.randint(0, 100)
    container[namespace] = {f"{key}": value}
    container.sync()
    assert container[f"{namespace}/{key}"].fetch() == value
    new_value = fake.name()
    with pytest.raises(ValueError):
        container[namespace] = {f"{key}": new_value}
        container.sync()