assert_same_test.rb

require 'minitest/autorun'
require 'allocation_tracer'

class MyTest < Minitest::Test
  def setup
    super
    @a = Object.new
    @b = Object.new
    @start = -GC.stat(:total_allocated_object)
  end

  def teardown
    p @start + GC.stat(:total_allocated_object)
    super
  end

  def test_same_ok
    assert_same @a, @a
  end

  def test_same_fail
    #assert_same @a, @b
  end
end

__END__

Before patch:

[aaron@higgins minitest (master)]$ ruby -Ilib test.rb 
Run options: --seed 55775

# Running:

0
.5
.

Finished in 0.002264s, 883.3922 runs/s, 441.6961 assertions/s

After patch:

[aaron@higgins minitest (master)]$ ruby -Ilib test.rb 
Run options: --seed 23530

# Running:

2
.0
.

Finished in 0.002271s, 880.6693 runs/s, 440.3347 assertions/s.

defer.diff

diff --git a/lib/minitest/assertions.rb b/lib/minitest/assertions.rb
index 9864d38..c9de55a 100644
--- a/lib/minitest/assertions.rb
+++ b/lib/minitest/assertions.rb
@@ -125,7 +125,7 @@ module Minitest
       msg ||= "Failed assertion, no message given."
       self.assertions += 1
       unless test then
-        msg = msg.call if Proc === msg
+        msg = msg.call if msg.respond_to? :call
         raise Minitest::Assertion, msg
       end
       true
@@ -325,14 +325,18 @@ module Minitest
       assert obj.respond_to?(meth), msg
     end
 
+    class Omg < Struct.new :act, :exp, :tc
+      def call
+        data = [tc.mu_pp(act), act.object_id, tc.mu_pp(exp), exp.object_id]
+        "Expected %s (oid=%d) to be the same as %s (oid=%d)" % data
+      end
+    end
+
     ##
     # Fails unless +exp+ and +act+ are #equal?
 
     def assert_same exp, act, msg = nil
-      msg = message(msg) {
-        data = [mu_pp(act), act.object_id, mu_pp(exp), exp.object_id]
-        "Expected %s (oid=%d) to be the same as %s (oid=%d)" % data
-      }
+      msg = message(msg, '.'.freeze, Omg.new(act, exp, self))
       assert exp.equal?(act), msg
     end
 
@@ -479,15 +483,19 @@ module Minitest
       assert false, msg
     end
 
+    class Msg < Struct.new :msg, :ending, :callable
+      def call
+        msg = msg.call.chomp(".") if Proc === msg
+        custom_message = "#{msg}.\n" unless msg.nil? or msg.to_s.empty?
+        "#{custom_message}#{callable.call}#{ending}"
+      end
+    end
+
     ##
     # Returns a proc that will output +msg+ along with the default message.
 
-    def message msg = nil, ending = ".", &default
-      proc {
-        msg = msg.call.chomp(".") if Proc === msg
-        custom_message = "#{msg}.\n" unless msg.nil? or msg.to_s.empty?
-        "#{custom_message}#{default.call}#{ending}"
-      }
+    def message msg = nil, ending = '.'.freeze, callable
+      Msg.new msg, ending, callable
     end
 
     ##