async def METHOD_NAME(subtests):
    """Ensures that `flatten` is always returning the correct type."""
    futures = [
        # Flattens:
        (
            RequiresContextFutureResult.from_value(
                RequiresContextFutureResult.from_value(1),
            ),
            RequiresContextFutureResult.from_value(1),
        ),
    ]
    for container, merged in futures:
        with subtests.test(container=container, merged=merged):
            assert await flatten(
                container,
            )(...) == await merged(...)