I know you said, "Nevermind," but I wanted to add this bit:

Don't forget about the third parameter to the assert messages. It is
very useful for either giving hints about the meaning of the
assertion, or to diagnose what went wrong, either of which can be
helpful for posterity.

It's important to know that assert_match(pat,obj) essentially matches
`obj.to_s =~ pat`. The output gives the impression that it's matching
`obj.inspect =~ pat`, but that's just sort of an artifact of
AssertionMessage#convert.

Here's some code/output:

require 'test/unit'
class Sampson
  def initialize
    @riddle = '"Out of the eater, something to eat;' +
      'out of the strong, something sweet."'
  end
  class PhilistineTest < Test::Unit::TestCase
    def test_quiz
      nazirite = Sampson.new
      pat = %r/eater/
      assert_match(pat, nazirite, "#{nazirite} !~ /#{pat}/")
    end
  end
end

Loaded suite /home/rking/src/scrap
Started
F
Finished in 0.047188 seconds.

  1) Failure:
test_quiz(Sampson::PhilistineTest) [/home/rking/src/scrap.rb:36]:
#<Sampson:0xb7ca2c74> !~ /(?-mix:eater)/.
<#<Sampson:0xb7ca2c74
 @riddle=
  "\"Out of the eater, something to eat;out of the strong, something
sweet.\"">> expected to be =~
</eater/>.

1 tests, 1 assertions, 1 failures, 0 errors

See that line immediately after the test_quiz(...) line? That's my
custom-provided line. It's kind of buried, but having it is at least
clearer than the lines below, which are a little misleading.

HTH,
-rking