function assertNode(node) {
  // `isPlainObj` unfortunately uses `any` instead of `unknown`.
  // type-coverage:ignore-next-line
  if (!isPlainObj(node) || typeof node.type !== 'string') {
    throw new TypeError('Expected node, got `' + node + '`')
    // Fine.
  }
}
Assert `node` is a unist node.

@param {unknown} node
@returns {asserts node is Node}