google_client.rb

require 'httparty'
require 'minitest/autorun'
require 'minitest/mock'

class GoogleClient

  BASE_URI = "http://google.com"

  attr_writer :http_client

  def initialize(http_client = nil)
    @http_client = http_client || HTTParty
  end

  def query(query_string)
    http_client.get(BASE_URI + '/search?q=' + query_string.tr(" ", "+"))
  end

  private

  def http_client
    @http_client
  end

end

class GoogleClientTest < Minitest::Test

  def test_calls_http_client_using_stub
    mock = Minitest::Mock.new
    mock.expect(:get, nil, ["http://google.com/search?q=cats"])
    client = GoogleClient.new

    client.stub(:http_client, mock) do
      client.query('cats')
    end

    mock.verify
  end

  def test_calls_http_client_using_constructor_injection
    mock = Minitest::Mock.new
    mock.expect(:get, nil, ["http://google.com/search?q=cats"])
    client = GoogleClient.new(mock)
    client.query('cats')
    mock.verify
  end

  def test_calls_http_client_using_setter_injection
    mock = Minitest::Mock.new
    mock.expect(:get, nil, ["http://google.com/search?q=cats"])
    client = GoogleClient.new
    client.http_client = mock
    client.query('cats')
    mock.verify
  end

end