gistfile1.rb

shared_context "for_extending" do
  context "extended with MyModule" do
    before(:all){ subject.extend(MyModule) }
    it "should define #some_method" do
      subject.should respond_to(:some_method)
    end
    yield
  end
end

describe Object do
  execute_context("for_extending")
end

describe Class do
  execute_context("for_extending") do
    it "should also define #special_method_for_class" do
      subject.should respond_to(:special_method_for_class)
    end
  end
end