def is_stub_body(node: LN) -> bool:
    """Return True if `node` is a simple statement containing an ellipsis."""
    if not isinstance(node, Node) or node.type != syms.simple_stmt:
        return False

    if len(node.children) != 2:
        return False

    child = node.children[0]
    return (
        not child.prefix.strip()
        and child.type == syms.atom
        and len(child.children) == 3
        and all(leaf == Leaf(token.DOT, ".") for leaf in child.children)
    )
Return True if `node` is a simple statement containing an ellipsis.
src/black/nodes.py