Maybe I'm just tired, but I first took this to mean that it was impossible for assert-same to be defined so that its arguments were (actual expected (o fail-message)). Now I realize that you just mean the positions of your expected/actual values are important.

One design thought: the name assert isn't taken by Arc. You could simplify the interface while generalizing it by just separating assert from the things it's asserting.

So, the basic assert would essentially be assert-t, and the other three could follow. Something like

  (assert-t actual (o fail-message))
  ; becomes
  (assert actual (o fail-message))
  ; or, without the custom message
  (assert actual)

  (assert-nil actual (o fail-message)) 
  ; becomes
  (assert (no actual) (o fail-message))
  ; or, without the custom message
  (assert:no actual)

  (assert-error actual (o expected-error))
  ; becomes
  (assert (error actual (o expected-error)) (o fail-message))
  ; or, without the custom message
  (assert:error actual (o expected-error))

  (assert-same expected actual (o fail-message))
  ; becomes
  (assert (same expected actual) (o fail-message))
  ; or, without the custom message
  (assert:same expected actual)

  (mac assert (condition (o fail-message))
    `(on-err (fn (c) ...fail...)
             (fn () (unless ,condition ...fail...))))

  (mac same (expected actual)
    (w/uniq (e a)
      `(with (,e ,expected ,a ,actual)
         (or (iso-that-works-on-hash-tables ,e ,a)
             (err "" ',actual 'returned ,a 'wanted ,e))))) ; modulo prettiness

  (mac error (expr (o expected-error))
    `(on-err (fn (c) ...pass, modulo expected-error...)
             (fn () ,expr ...fail if we get here without an error...)))

I'm not sure of my feelings on changing all the asserts to be just one. On one hand, it is simpler to have just the one command. On the other, it seems like a much more complicated interface, as you would never guess how to use it from, for example, the method signature. assert-t, assert-same et. al. seem like a lower conceptual load.

One thing that fell out of this is that there's no built-in way that I know of to check hashes for equality in Arc. Even `iso` doesn't do it (https://bitbucket.org/zck/unit-test.arc/issue/18/make-assert...). So I wrote a way (https://bitbucket.org/zck/unit-test.arc/commits/a007eb6491c3...).

The only big thing that I really want to do for usability right now is to not have a ton of lines of "test X passed!" (https://bitbucket.org/zck/unit-test.arc/issue/20/optionally-...).