Before:
  " Switch to the test rails directory.
  let b:path = getcwd()
  silent! cd /testplugin/test/handler

  runtime ale_linters/perl/perl.vim

After:
  silent! 'cd ' . fnameescape(b:path)
  unlet! b:path

  call ale#linter#Reset()

Execute(The Perl linter should ignore errors from other files):
  silent! noautocmd file bar.pl

  AssertEqual
  \ [
  \    {'lnum': '2', 'type': 'E', 'text': 'Compilation failed in require'},
  \ ],
  \ ale_linters#perl#perl#Handle(bufnr(''), [
  \   'syntax error at ' . b:path . '/foo.pm line 4, near "aklsdfjmy "',
  \   'Compilation failed in require at ' . b:path . '/bar.pl line 2.',
  \   'BEGIN failed--compilation aborted at ' . b:path . '/bar.pl line 2.',
  \ ])