Before:
  let g:history = []
  let g:ale_buffer_info = {}
  let g:ale_max_buffer_history_size = 20

  function! CollectResults(buffer, output)
    return []
  endfunction

  call ale#linter#Define('foobar', {
  \ 'name': 'testlinter',
  \ 'callback': 'CollectResults',
  \ 'executable': 'echo',
  \ 'command': 'echo command history test',
  \ 'read_buffer': 0,
  \})

After:
  let g:ale_history_enabled = 1
  unlet g:history
  let g:ale_buffer_info = {}
  let g:ale_max_buffer_history_size = 20
  call ale#linter#Reset()
  delfunction CollectResults

Given foobar (Some imaginary filetype):
  anything

Execute(History should be set when commands are run):
  AssertEqual 'foobar', &filetype

  call ale#Lint()
  call ale#engine#WaitForJobs(2000)

  let g:history = g:ale_buffer_info[bufnr('%')].history

  AssertEqual 1, len(g:history)
  AssertEqual ['status', 'job_id', 'command'], keys(g:history[0])
  AssertEqual ['/bin/bash', '-c', 'echo command history test'], g:history[0].command
  AssertEqual 'started', g:history[0].status
  " The Job ID will change each time, but we can check the type.
  AssertEqual type(1), type(g:history[0].job_id)

Execute(History should be not set when disabled):
  AssertEqual 'foobar', &filetype

  let g:ale_history_enabled = 0

  call ale#Lint()
  call ale#engine#WaitForJobs(2000)

  AssertEqual 0, len(g:ale_buffer_info[bufnr('%')].history)

Execute(History items should be popped after going over the max):
  let g:ale_buffer_info[1] = {
  \ 'history': map(range(20), '{''status'': ''started'', ''job_id'': v:val, ''command'': ''foobar''}'),
  \}

  call ale#history#Add(1, 'started', 347, 'last command')

  AssertEqual
  \ (
  \   map(range(1, 19), '{''status'': ''started'', ''job_id'': v:val, ''command'': ''foobar''}')
  \   + [{'status': 'started', 'job_id': 347, 'command': 'last command'}]
  \ ),
  \ g:ale_buffer_info[1].history

Execute(Nothing should be added to history if the size is too low):
  let g:ale_max_buffer_history_size = 0
  let g:ale_buffer_info[1] = {'history': []}

  call ale#history#Add(1, 'started', 347, 'last command')

  AssertEqual [], g:ale_buffer_info[1].history

  let g:ale_max_buffer_history_size = -2

  call ale#history#Add(1, 'started', 347, 'last command')

  AssertEqual [], g:ale_buffer_info[1].history