It'd be good if `a2ps-check-buffer' saved the buffer before running the
check on the file. I like a blob with `save-some-buffers' so that it
prompts you that it's going to save.
(let ((a2ps-check-buffer--target (current-buffer)))
(save-some-buffers nil (lambda ()
(equal (current-buffer)
a2ps-check-buffer--target))))