react-check-on-props.jsx

function MenuButton({ children }) {
  let called = false
  function getButtonProps(props) {
    const merged = merge({
      onClick: () => {},
      role: 'button',
    }, props)
    called = true
    return merged
  }
  const rendered = children({ getButtonProps })
  if (!called) {
   throw new Error('must call getButtonProps')
  }
  return rendered
}