mock Rails.env.development? using rspec

Question

I am writing a unit test using rspec.

I would like to mock Rails.env.develepment? to return true. How could I achieve this?.

I tried this

Rails.env.stub(:development?, nil).and_return(true)

it throws this error

activesupport-4.0.0/lib/active_support/string_inquirer.rb:22:in `method_missing': undefined method `any_instance' for "test":ActiveSupport::StringInquirer (NoMethodError)

Update ruby version ruby-2.0.0-p353, rails 4.0.0, rspec 2.11

describe "welcome_signup" do
    let(:mail) { Notifier.welcome_signup user }

    describe "in dev mode" do
      Rails.env.stub(:development?, nil).and_return(true)
      let(:mail) { Notifier.welcome_signup user }
      it "send an email to" do
        expect(mail.to).to eq([GlobalConstants::DEV_EMAIL_ADDRESS])
      end
    end
  end

Answer 1

There is a much better way described here: https://stackoverflow.com/a/24052647/362378

it "should do something specific for production" do 
  allow(Rails).to receive(:env) { "production".inquiry }
  #other assertions
end

This will provide all the functions like Rails.env.test? and also works if you just compare the strings like Rails.env == 'production'