Before:
  Save g:ale_max_signs

  let g:ale_max_signs = -1

  function! SetNProblems(sign_count)
    let l:loclist = []
    let l:range = range(1, a:sign_count)
    call setline(1, l:range)

    for l:index in l:range
      call add(l:loclist, {
      \ 'bufnr': bufnr(''),
      \ 'lnum': l:index,
      \ 'col': 1,
      \ 'type': 'E',
      \ 'text': 'a',
      \})
    endfor

    call ale#sign#SetSigns(bufnr(''), l:loclist)

    return sort(map(ale#sign#FindCurrentSigns(bufnr(''))[1], 'v:val[0]'), 'n')
  endfunction

After:
  Restore

  unlet! b:ale_max_signs

  delfunction SetNProblems

  sign unplace *

Execute(There should be no limit on signs with negative numbers):
  AssertEqual range(1, 42), SetNProblems(42)

Execute(0 signs should be set when the max is 0):
  let g:ale_max_signs = 0

  AssertEqual [], SetNProblems(42)

Execute(1 signs should be set when the max is 1):
  let g:ale_max_signs = 1

  AssertEqual [1], SetNProblems(42)

Execute(10 signs should be set when the max is 10):
  let g:ale_max_signs = 10

  " We'll check that we set signs for the first 10 items, not other lines.
  AssertEqual range(1, 10), SetNProblems(42)

Execute(5 signs should be set when the max is 5 for the buffer):
  let b:ale_max_signs = 5

  AssertEqual range(1, 5), SetNProblems(42)