open_session can just return the a dup of the current context.

At this point, its entire purpose in the open_session {} case was to
delegate back to the IntegrationTest anyway.

actionpack/lib/action_dispatch/testing/integration.rb

@@ -297,7 +297,7 @@ module ActionDispatch
       # Reset the current session. This is useful for testing multiple sessions
       # in a single test case.
       def reset!
-        @integration_session = open_session
+        @integration_session = Integration::Session.new(app)
       end
 
       %w(get post put head delete cookies assigns
@@ -323,30 +323,9 @@ module ActionDispatch
       # can use this method to open multiple sessions that ought to be tested
       # simultaneously.
       def open_session(app = nil)
-        session = Integration::Session.new(app || self.app)
-
-        # delegate the fixture accessors back to the test instance
-        extras = Module.new { attr_accessor :delegate, :test_result }
-        if self.class.respond_to?(:fixture_table_names)
-          self.class.fixture_table_names.each do |table_name|
-            name = table_name.tr(".", "_")
-            next unless respond_to?(name)
-            extras.__send__(:define_method, name) { |*args|
-              delegate.send(name, *args)
-            }
-          end
+        dup.tap do |session|
+          yield session if block_given?
         end
-
-        # delegate add_assertion to the test case
-        extras.__send__(:define_method, :add_assertion) {
-          test_result.add_assertion
-        }
-        session.extend(extras)
-        session.delegate = self
-        session.test_result = @_result
-
-        yield session if block_given?
-        session
       end
 
       # Copy the instance variables from the current session instance into the

actionpack/test/controller/integration_test.rb

@@ -173,14 +173,12 @@ class IntegrationTestTest < Test::Unit::TestCase
   end
 
   def test_opens_new_session
-    @test.class.expects(:fixture_table_names).times(2).returns(['foo'])
-
     session1 = @test.open_session { |sess| }
     session2 = @test.open_session # implicit session
 
-    assert_kind_of ::ActionController::Integration::Session, session1
-    assert_kind_of ::ActionController::Integration::Session, session2
-    assert_not_equal session1, session2
+    assert session1.respond_to?(:assert_template), "open_session makes assert_template available"
+    assert session2.respond_to?(:assert_template), "open_session makes assert_template available"
+    assert !session1.equal?(session2)
   end
 
   # RSpec mixes Matchers (which has a #method_missing) into