next.js/test/e2e/app-dir/actions/app/form/page.js

import { accountForOverhead } from '../../account-for-overhead'

async function action(formData) {
  'use server'
  const payload = formData.get('payload').toString()
  console.log('size =', payload.length)
}

export default function Page() {
  return (
    <>
      <form action={action}>
        <input
          type="hidden"
          name="payload"
          value={'a'.repeat(accountForOverhead(1))}
        />
        <button type="submit" id="size-1mb">
          SUBMIT 1mb
        </button>
      </form>
      <form action={action}>
        <input
          type="hidden"
          name="payload"
          value={'a'.repeat(accountForOverhead(2))}
        />
        <button type="submit" id="size-2mb">
          SUBMIT 2mb
        </button>
      </form>
      <form action={action}>
        <input
          type="hidden"
          name="payload"
          value={'a'.repeat(accountForOverhead(3))}
        />
        <button type="submit" id="size-3mb">
          SUBMIT 3mb
        </button>
      </form>
    </>
  )
}