Test with a mock and a stub

test_my_class.rb

require "minitest/autorun"

class RestClient
  def self.get action
  end
end

class MyClass
  def do_it!
    RestClient.get :index
  end
end

class TestMyClass < Minitest::Test
  def test_mock_and_stub
    mock = Minitest::Mock.new
    mock.expect :does_something, "return value"

    RestClient.stub :get, :index do
      mock.does_something
    end

    MyClass.new.do_it!

    mock.verify
  end
end