Deprecate RSpec::Mocks::TestDouble.extend_onto

Changelog.md

@@ -1,6 +1,10 @@
 ### 2.99.0.rc1 Development
 [full changelog](http://github.com/rspec/rspec-mocks/compare/v2.99.0.beta2...2-99-maintenance)
 
+Deprecations:
+
+* Deprecate `RSpec::Mocks::TestDouble.extend_onto`. (Myron Marston)
+
 ### 2.99.0.beta2 / 2014-02-17
 [full changelog](http://github.com/rspec/rspec-mocks/compare/v2.99.0.beta1...v2.99.0.beta2)
 

lib/rspec/mocks/test_double.rb

@@ -13,6 +13,7 @@ module TestDouble
       #   RSpec::Mocks::TestDouble.extend_onto(module, "MyMixin", :foo => "bar")
       #   module.foo  #=> "bar"
       def self.extend_onto(object, name=nil, stubs_and_options={})
+        RSpec.deprecate("`RSpec::Mocks::TestDouble.extend_onto(...)`")
         object.extend self
         object.send(:__initialize_as_test_double, name, stubs_and_options)
       end

spec/rspec/mocks/test_double_spec.rb

@@ -3,6 +3,8 @@
 module RSpec
   module Mocks
     describe TestDouble do
+      before { allow_deprecation }
+
       before(:all) do
         Module.class_eval do
           private
@@ -31,6 +33,11 @@ def use; end
         expect { double.foo }.to raise_error(/Mock "MyDouble" received/)
       end
 
+      it 'warns when `extend_onto` is used' do
+        expect_deprecation_with_call_site(__FILE__, __LINE__ + 1, /RSpec::Mocks::TestDouble.extend_onto/)
+        Module.new { TestDouble.extend_onto(self) }
+      end
+
       [[:should, :expect], [:expect], [:should]].each do |syntax|
         context "with syntax #{syntax.inspect}" do
           include_context "with syntax", syntax

spec/spec_helper.rb

@@ -37,7 +37,7 @@ def expect_warn_deprecation_with_call_site(file, line, snippet=//)
   end
 
   def allow_deprecation
-    allow(RSpec.configuration.reporter).to receive(:deprecation)
+    RSpec::Mocks.allow_message(RSpec.configuration.reporter, :deprecation)
   end
 
   def allow_unavoidable_1_8_deprecation