Add test for stubbing class method defined on module & aliased

This test was derived from the tests in #244 and was failing before we
moved to always (in Ruby v2+) using the prepended module stubbing
mechanism. We'll probably want to expand it to cover some more
scenarios, but it's useful as it stands.

This test fails in Ruby 1.8.x and we can't find an obvious fix.

The test passes in Ruby 1.9.x due to a change in behaviour of `#owner`
when a class is `extend`ed by a module.

The test passes in Rubies > 2.0 because we now always prepend a module
to avoid overwriting the original method at all.

test/acceptance/stub_method_defined_on_module_and_aliased_test.rb

@@ -0,0 +1,39 @@
+require File.expand_path('../acceptance_test_helper', __FILE__)
+require 'mocha/setup'
+
+unless Mocha::PRE_RUBY_V19
+  class StubMethodDefinedOnModuleAndAliasedTest < Mocha::TestCase
+    include AcceptanceTest
+
+    def setup
+      setup_acceptance_test
+    end
+
+    def teardown
+      teardown_acceptance_test
+    end
+
+    def test_stubbing_class_method_defined_by_aliasing_module_instance_method
+      mod = Module.new do
+        def module_instance_method
+          'module-instance-method'
+        end
+      end
+
+      klass = Class.new do
+        extend mod
+        class << self
+          alias_method :aliased_module_instance_method, :module_instance_method
+        end
+      end
+
+      assert_snapshot_unchanged(klass) do
+        test_result = run_as_test do
+          klass.stubs(:aliased_module_instance_method).returns('stubbed-aliased-module-instance-method')
+          assert_equal 'stubbed-aliased-module-instance-method', klass.aliased_module_instance_method
+        end
+        assert_passed(test_result)
+      end
+    end
+  end
+end