This passes on all Emacs versions until 24.2, but fails on trunk:

eme> emacs-24.2 -batch -Q -l eme.el
Running 1 tests (2013-05-19 16:16:06+0200)
   passed  1/1  surprise

Ran 1 tests, 1 results as expected (2013-05-19 16:16:06+0200)

eme> emacs-24.3.50 -batch -Q -l eme.el
Running 1 tests (2013-05-19 16:16:16+0200)
Test surprise backtrace:
  (if (unwind-protect (setq value-2 (apply fn-0 args-1)) (setq form-de
  (let (form-description-4) (if (unwind-protect (setq value-2 (apply f
  (let ((value-2 (quote ert-form-evaluation-aborted-3))) (let (form-de
  (let ((fn-0 (function equal)) (args-1 (list (quote ((one . two) one)
  (lambda nil (let ((fn-0 (function equal)) (args-1 (list (quote ((one
  #[0 "\306\307!r\211q\210\310\311\312\313\314\315!\316\"\317\320%DC
  funcall(#[0 "\306\307!r\211q\210\310\311\312\313\314\315!\316\"\31
  ert--run-test-internal([cl-struct-ert--test-execution-info [cl-struc
  #[0 "r\304\305!q\210\306 )\307\310\311\312\313\314!\315\"\316\317%
  funcall(#[0 "r\304\305!q\210\306 )\307\310\311\312\313\314!\315\"\
  ert-run-test([cl-struct-ert-test surprise nil (lambda nil (let ((fn-
  ert-run-or-rerun-test([cl-struct-ert--stats surprise [[cl-struct-ert
  ert-run-tests(surprise #[385 "\306\307\"\203D\211\211G\310U\203\
  ert-run-tests-batch(surprise)
  ert-run-tests-batch-and-exit(surprise)
  eval-buffer(#<buffer  *load*> nil "/eme/eme.el"
  load-with-code-conversion("/eme/eme.el" "/eme/
  load("/eme/eme.el" nil t)
  command-line-1(("-l" "eme.el"))
  command-line()
  normal-top-level()
Test surprise condition:
    (ert-test-failed
     ((should
       (equal '...
        (progn ... ... ll)))
      :form
      (equal
       ((one . two)
        one)
       (two one))
      :value nil :explanation
      (list-elt 0
                (different-types
                 (one . two)
                 two))))
   FAILED  1/1  surprise

Ran 1 tests, 0 results as expected, 1 unexpected (2013-05-19 16:16:16+0200)

1 unexpected results:
   FAILED  surprise


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

Wavetables for the Waldorf Blofeld:
http://Synth.Stromeko.net/Downloads.html#BlofeldUserWavetables