#let assert-eq(a, b) = assert(a == b)

#let assert-grid(state, file, rank, expected) = {
  let actual = state.grid.at(8 - rank).at(file - 1)
  assert(actual == expected)
}

#let assert-no-error(state, label) = {
  let err = state.at("error", default: none)
  assert(err == none)
}

#let assert-error(state, expected) = {
  let err = state.at("error", default: none)
  assert(err != none)
  assert(err == expected)
}