How to test a client for a backend app. Creates a simple app, simple client, consumes it with rack-test, starts it up on a server, consumes it with restclient.

testing_a_client_for_a_backend_app.rb

# backend app
require 'sinatra/base'
require 'json'
class UsersController < Sinatra::Base
  get '/users/:id' do
    JSON.dump id: params[:id].to_i, name: "Josh"
  end
end



# a client to consume the backend app
require 'json'
class UsersClient
  User = Struct.new :id, :name
  
  def initialize(attributes)
    @the_internetz = attributes.fetch :the_internetz
    @base_url      = attributes.fetch :base_url
  end
  
  def find(id)
    response        = @the_internetz.get @base_url + "/users/#{id}"
    user_attributes = JSON.parse response.body
    User.new user_attributes['id'], user_attributes['name']
  end
end



# test the client without needing to start a server
require 'rack/test'           
test_client = UsersClient.new the_internetz: Rack::Test::Session.new(UsersController),
                              base_url:      ''
user = test_client.find(12)
user.id    # => 12
user.name  # => "Josh"



# use the client for real
require 'restclient'
require 'webrick'
server_thread = Thread.new do
  Rack::Server.start app: UsersController, Port: 8080, server: 'webrick', Logger: WEBrick::Log.new($stdout)
end
sleep 2 # let the server start
real_client = UsersClient.new the_internetz: RestClient,
                              base_url:      'http://localhost:8080'
user = real_client.find(12)
user.id   # => 12
user.name # => "Josh"

server_thread.kill

# >> [2014-04-18 14:40:13] INFO  WEBrick 1.3.1
# >> [2014-04-18 14:40:13] INFO  ruby 2.1.1 (2014-02-24) [x86_64-darwin13.0]
# >> [2014-04-18 14:40:13] INFO  WEBrick::HTTPServer#start: pid=28022 port=8080
# >> [2014-04-18 14:40:15] INFO  going to shutdown ...

# !> localhost - - [18/Apr/2014:14:40:15 MDT] "GET /users/12 HTTP/1.1" 200 23
# !> - -> /users/12

we used the same approach for a few projects, check out: https://github.com/jsl/shamrock