Before:
  runtime ale_linters/lilypond/lilypond.vim
  call ale#linter#Reset()

Execute(The lilypond handler should parse a single error correctly):
  AssertEqual
  \ [
  \   {
  \     'lnum': 2,
  \     'col': 5,
  \     'type': 'E',
  \     'text': 'syntax error, unexpected NOT_A_TOKEN',
  \   }
  \ ],
  \ ale_linters#lilypond#lilypond#Handle(0, [
  \   'test.ly:2:5: error: syntax error, unexpected NOT_A_TOKEN'
  \ ])

Execute(The lilypond handler should parse warnings and errors):
  AssertEqual
  \ [
  \   {
  \     'lnum': 3,
  \     'col': 1,
  \     'type': 'W',
  \     'text': 'deprecated syntax',
  \   },
  \   {
  \     'lnum': 5,
  \     'col': 12,
  \     'type': 'E',
  \     'text': 'unknown symbol',
  \   }
  \ ],
  \ ale_linters#lilypond#lilypond#Handle(0, [
  \   'test.ly:3:1: warning: deprecated syntax',
  \   'test.ly:5:12: error: unknown symbol'
  \ ])

Execute(The lilypond handler should ignore non-matching lines):
  AssertEqual
  \ [],
  \ ale_linters#lilypond#lilypond#Handle(0, [
  \   'This is some unrelated output',
  \   'Another line without structure'
  \ ])

After:
  call ale#linter#Reset()