omniauth_macros.rb

# in spec/support/omniauth_macros.rb
module OmniauthMacros
  def mock_auth_hash
    # The mock_auth configuration allows you to set per-provider (or default)
    # authentication hashes to return during integration testing.
    OmniAuth.config.mock_auth[:twitter] = {
      'provider' => 'twitter',
      'uid' => '123545',
      'user_info' => {
        'name' => 'mockuser',
        'image' => 'mock_user_thumbnail_url'
      },
      'credentials' => {
        'token' => 'mock_token',
        'secret' => 'mock_secret'
      }
    }
  end
end

spec_helper.rb

# in spec/requests/spec_helper.rb
RSpec.configure do |config|
  # ...
  # include our macro
  config.include(OmniauthMacros)
end

OmniAuth.config.test_mode = true

top_spec.rb

# in spec/requests/top_spec.rb
describe "access top page" do
  it "can sign in user with Twitter account" do
    visit '/'
    page.should have_content("Sign in with Twitter")
    mock_auth_hash
    click_link "Sign in"
    page.should have_content("mockuser")  # user name
    page.should have_css('img', :src => 'mock_user_thumbnail_url') # user image
    page.should have_content("Sign out")
  end

  it "can handle authentication error" do
    OmniAuth.config.mock_auth[:twitter] = :invalid_credentials
    visit '/'
    page.should have_content("Sign in with Twitter")
    click_link "Sign in"
    page.should have_content('Authentication failed.')
  end

end