After:
  unlet! g:buffer
  let g:ale_buffer_info = {}

Execute('ALE globals should be cleared when the buffer is deleted):
  new

  let g:ale_buffer_info = {
  \  bufnr(''): {'temporary_file_list': [], 'temporary_directory_list': []},
  \  10347: {'temporary_file_list': [], 'temporary_directory_list': []},
  \}

  bdelete
  AssertEqual {10347: {'temporary_file_list': [], 'temporary_directory_list': []}}, g:ale_buffer_info