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_why just blogged about my xmp code annotator for Ruby and shot the following idea

You know what would be wild? To use this as a way of writing test cases. You write the code that needs to be tested and annotate it with the asserts.

So here is a rough implementation... the enhanced^3 xmp filter will now turn

 require 'test/unit'
 class Foo
   class StillTooSmallWheresYourManhoodDude < Exception; end
   attr_reader :b
   def initialize; @a = [] end
   def foo(x); @a << x end
   def bar; @a.join(" ") end
   def baz; @a.size end
   def foobar; raise StillTooSmallWheresYourManhoodDude unless @a.size > 6; "OK" end
 end

 class TestFoo < Test::Unit::TestCase
   def setup; @f = Foo.new end
   def test_basic_foo
     @f.foo 1
     @f.bar # =>
     @f.baz # =>
     @f.b # =>
   end

   def test_more_foo
     @f.foobar # =>
     10.times{|i| @f.foo i }
     @f.bar # =>
     @f.foobar # =>
   end
 end

into

 require 'test/unit'
 class Foo
   class StillTooSmallWheresYourManhoodDude < Exception; end
   attr_reader :b
   def initialize; @a = [] end
   def foo(x); @a << x end
   def bar; @a.join(" ") end
   def baz; @a.size end
   def foobar; raise StillTooSmallWheresYourManhoodDude unless @a.size > 6; "OK" end
 end

 class TestFoo < Test::Unit::TestCase
   def setup; @f = Foo.new end
   def test_basic_foo
     @f.foo 1
     assert_equal("1", @f.bar)
     assert_equal(1, @f.baz)
     assert_nil(@f.b)
   end

   def test_more_foo
     assert_raise(Foo::StillTooSmallWheresYourManhoodDude){@f.foobar}
     10.times{|i| @f.foo i }
     assert_equal("0 1 2 3 4 5 6 7 8 9", @f.bar)
     assert_equal("OK", @f.foobar)
   end
 end
 # >> "Loaded suite -\nStarted\n..\nFinished in 0.000819 seconds.\n\n2 tests, 0 assertions, 0 failures, 0 errors\n"