gistfile1.rb

# In config/initializers/local_override.rb:

require 'devise/strategies/authenticatable'

module Devise
  module Strategies
    class LocalOverride < Authenticatable
      def valid?
        true
      end

      def authenticate!
        if params[:user]
          user = User.find_by_email(params[:user][:email])

          if user && user.encrypted_password == params[:user][:password]
            success!(user)
          else
            fail
          end 
        else
          fail
        end 
      end 
    end 
  end 
end

Warden::Strategies.add(:local_override, Devise::Strategies::LocalOverride)



# In config/initializers/devise.rb

config.warden do |manager|
  manager.default_strategies(:scope => :user).unshift :local_override
end


# In spec/path_to_test_spec.rb

# I do this in before block or right before test executes
@request = mock(:request)
@strategy = Devise::Strategies::AndroidAuthenticatable.new(nil)
@request.should_receive(:headers).and_return({#hash of the headers you are testing})
@strategy.should_receive(:params).at_least(:once).and_return({#hash of the params})
@strategy.should_receive(:request).and_return(@request)

# Break these up as needed to test failing and successful 
# strategies for your application
lambda {
   @strategy.should be_valid
   @strategy.authenticate!.should eql :success 
}.should_not raise_error