Before:
    " Load the file which defines the linter.
  runtime ale_linters/sql/sqllint.vim

After:
    " Unload all linters again.
  call ale#linter#Reset()

Execute (The output should be correct):

  " Test that the right loclist items are parsed from the handler.
  AssertEqual
  \ [
  \   {
  \     'lnum': 1,
  \     'col': 0,
  \     'type': '',
  \     'text': 'stdin:1 [ER_NO_DB_ERROR] No database selected'
  \   },
  \ ],
  \ ale_linters#sql#sqllint#Handle(bufnr(''), [
  \  'stdin:1 [ER_NO_DB_ERROR] No database selected'
  \ ])