Service Double

A tool for making fake versions of external (web) services. You can use fake web services to return predicatable results for testing.

What you need to do is create a small Sinatra application, that will play the fake version during your tests.

By convention, the application should respond to two basic urls: GET / and DELETE /. The GET request is used to tell if the application is running. The DELETE request should reset the application, and is called between each test/scenario.

An example of such a fake web service:

values = []

get "/" do
  200
end

delete "/" do
  values.clear
  200
end

post "/remember" do
  values << params[:value]
end

get "/remembered" do
  { :remembered => values }.to_json
end

The idea is that inside this fake app, you can cheat all you like. Your database might be a simple hash or array, or you can choose to return simple canned responses.

You can also add paths to your fake app that don't exist in the real app, which you can use for easy testing and debugging.

Add this line to your application's Gemfile:

group :test do
  gem 'service_double', require: false
end

And then execute:

$ bundle

Or install it yourself as:

$ gem install service_double

To hook it up to a test framework:

require 'service_double'

ServiceDouble.hook_into(:cucumber) do |config|
  config.server = "my_sinatra_server.rb"
  config.url = "http://localhost:12345"
end

Supported frameworks are currently :cucumber and :rspec.

The configuration options are:

• server where to find the fake web service app (required)
• url where the fake web service should be accessed (required)
• timeout how long you allow the fake server to take booting up (default: 2 seconds)
• log_file where to write the server logs to (default: "log/#{server}.log")

You can have one or multiple services doubles, and control them:

$widget_service = ServiceDouble.hook_into(:rspec) do |config|
  config.server = "fake_widgets.rb"
  config.url = "http://localhost:12345"
end

$weather_service = ServiceDouble.hook_into(:rspec) do |config|
  config.server = "fake_weather.rb"
  config.url = "http://localhost:12346"
end

# later on:

$weather_service.post("/_stub_temp", :place => "New York", :temp => 22.4)

Here are some methods that can be called on the service objects:

• get performs a GET request (maps to Faraday's get method)
• post performs a POST request (like get)
• delete etc...
• put etc...
• post etc...
• reset sends DELETE request to / (is done automatically between tests)

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request