use failure messages from rails assertions when delegating to them

lib/rspec/rails/matchers.rb

@@ -23,13 +23,21 @@ class AssertionFailedError < StandardError
   match_unless_raises Test::Unit::AssertionFailedError do |_|
     assert_redirected_to destination
   end
+
+  failure_message_for_should do
+    rescued_exception.message
+  end
 end
 
 RSpec::Matchers.define :render_template do |options, message|
   match_unless_raises Test::Unit::AssertionFailedError do |_|
     options = options.to_s if Symbol === options
     assert_template options, message
   end
+
+  failure_message_for_should do
+    rescued_exception.message
+  end
 end
 
 RSpec::Matchers.define :be_a_new do |model_klass|

spec/rspec/rails/matchers/redirect_to_spec.rb

@@ -1,8 +1,18 @@
 require "spec_helper"
+require "action_controller/test_case"
 
 describe "redirect_to" do
   it "delegates to assert_redirected_to" do
     self.should_receive(:assert_redirected_to).with("destination")
     "response".should redirect_to("destination")
   end
+
+  it "uses failure message from assert_redirected_to" do
+    self.stub!(:assert_redirected_to).and_raise(
+      Test::Unit::AssertionFailedError.new("this message"))
+    response = ActionController::TestResponse.new
+    expect do
+      response.should redirect_to("destination")
+    end.to raise_error("this message")
+  end
 end

spec/rspec/rails/matchers/render_template_spec.rb

@@ -1,6 +1,15 @@
 require "spec_helper"
 
 describe "render_template" do
+  it "uses failure message from render_template" do
+    self.stub!(:assert_template).and_raise(
+      Test::Unit::AssertionFailedError.new("this message"))
+    response = ActionController::TestResponse.new
+    expect do
+      response.should render_template("destination")
+    end.to raise_error("this message")
+  end
+
   context "given a hash" do
     it "delegates to assert_template" do
       self.should_receive(:assert_template).with({:this => "hash"}, "this message")