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Extension for webmock to make stubbed methods.
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Webmock Method

Gem-extension for webmock gem for creating services with mocked methods.

Installation

Add this line to your application's Gemfile:

gem 'webmock_method'

And then execute:

$ bundle

Or install it yourself as:

$ gem install webmock_method

Usage

[WebMock] (https://github.com/bblimke/webmock) is gem for stubbing HTTP requests. You can use it in your tests if you don't want to hit actual service while testing other functionality of your service. For example:

require 'webmock'

WebMock.stub_request(:any, "www.example.com").to_return(:body => "some body")

expect(Net::HTTP.get("www.example.com", "/")).to eq "some body"

It will stub all http verbs (GET, POST, PUT etc.) thanks to :any parameter.

You can also use webmock library for building stubbed versions of your services. This approach is especially useful when services to be called are not implemented yet (maybe by another team) and you still want to start working on your part and finish it on time.

In order to facilitate the creation of mocked service methods, you can use webmock_method gem.

How to use it?

First, create actual service wrapper that works with future API of "not yet developed service". As an example, we can use publicly available OpenWeatherMap web service.

We will implement call to quote weather for a given city. You have to provide location and units parameters:

# services/open_weather_map_service.rb

require 'net/http'

class OpenWeatherMapService
  attr_reader :url

  def initialize
    @url = 'http://api.openweathermap.org/data/2.5/weather'
  end

  def quote location, units
    quote_url = "#{url}?q=#{location}%20nj&units=#{units}"

    uri = URI.parse(URI.escape(quote_url))

    Net::HTTP.get(uri) # At this moment, service is not developed yet...
  end
end

Then, create stub/mock for your service:

# stubs/open_weather_map_service.rb

require 'webmock_method'

require 'services/open_weather_map_service.rb'

class OpenWeatherMapService
  extend WebmockMethod

  webmock_method :quote, [:location, :units],
    lambda { |_|
      File.open "#{File.dirname(__FILE__)}/stubs/templates/quote_response.json.erb"
    }, /#{WebmockMethod.url}/
end

webmock_method requires you to provide the following information:

  • method name to be mocked;
  • parameters names for the method (same as in original service);
  • proc/lambda expression for building the response;
  • url to remote service (optional).

You can build responses of arbitrary complexity with your own code or you can use RenderHelper, that comes with this gem. Currently it supports erb and haml renderers only. Here is example of how to build xml response:

  webmock_method :purchase, [:amount, :credit_card],
    lambda { |binding|
      RenderHelper.render :erb, "#{File.dirname(__FILE__)}/templates/purchase_response.xml.erb", binding
    }

It's possible to tweak your response on the fly:

  webmock_method :purchase, [:amount, :credit_card],
    lambda { |binding|
      RenderHelper.render :erb, "#{File.dirname(__FILE__)}/templates/purchase_response.xml.erb", binding
    } do |parent, _, credit_card|
    if credit_card.card_type == "VISA"
      define_attribute(parent, :success,  true)
    else
      define_attribute(parent, :success,  false)
      define_attribute(parent, :error_message, "Unsupported Credit Card Type")
    end
  end

and then, use newly defined attributes, such as success and error_message inside your template:

<!-- stubs/templates/purchase_response.xml.erb -->
<PurchaseResponse>
  <Success><%= success %></Success>

  <% unless success %>
    <ErrorMessage><%= error_message %></ErrorMessage>
  <% end %>
</PurchaseResponse>

url parameter is optional. If you don't specify it, gem will try to use url attribute defined on your service or you can define url parameter for WebmockMethod:

WebmockMethod.url = "http://api.openweathermap.org/data/2.5/weather"

And finally, create spec for testing your mocked service:

require 'json'

require "stubs/open_weather_map_service"

describe OpenWeatherMapService do
  describe "#quote" do
    it "gets the quote" do
      result = JSON.parse(subject.quote("plainsboro, nj", "imperial"))

      expect(result['sys']['country']).to eq("United States of America")
    end
  end
end

If you need to simulate exception raised inside the mocked method, do the following:

  webmock_method :purchase, [:amount, :credit_card],
                 lambda { |binding|
                    # prepare response
                    ...
                  } do |parent, amount, credit_card|
    define_attribute(parent, :error, create_error(parent, "Negative amount")) if amount < 0

    ...
  end

  def self.create_error parent, reason
    define_attribute(parent, :error, Exception.new(reason))
  end

end

webmock gem code is aware of error variable and will throw this exception, so yo can verify it inside your test:

  it "returns error response if amount is negative" do
    expect{subject.purchase(-1000, valid_credit_card)}.to raise_exception(Exception)
  end

Contributing

  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