Mocha  
 
Description
- A Ruby library for mocking and stubbing - but deliberately not (yet) faking or spying.
- A unified, simple and readable syntax for both full & partial mocking.
- Built-in support for Minitest and Test::Unit.
- Supported by many other test frameworks.
Intended Usage
Mocha is intended to be used in unit tests for the Mock Object or Test Stub types of Test Double, not the Fake Object or Test Spy types. Although it would be possible to extend Mocha to allow the implementation of fakes and spies, we have chosen to keep it focused on mocks and stubs.
Installation
Gem
Install the latest version of the gem with the following command...
$ gem install mocha
Note: If you are intending to use Mocha with Test::Unit or Minitest, you should only setup Mocha after loading the relevant test library...
Test::Unit
require 'rubygems'
gem 'mocha'
require 'test/unit'
require 'mocha/test_unit'
Minitest
require 'rubygems'
gem 'mocha'
require 'minitest/autorun'
require 'mocha/minitest'
Bundler
If you're using Bundler, include Mocha in the Gemfile and then setup Mocha later once you know the test library has been loaded...
Test::Unit
# Gemfile
gem 'mocha'
# Elsewhere after Bundler has loaded gems e.g. after `require 'bundler/setup'`
require 'test/unit'
require 'mocha/test_unit'
Minitest
# Gemfile
gem 'mocha'
# Elsewhere after Bundler has loaded gems e.g. after `require 'bundler/setup'`
require 'minitest/autorun'
require 'mocha/minitest'
RSpec
RSpec includes a mocha adapter. Just tell RSpec you want to mock with :mocha:
# Gemfile in Rails app
gem 'mocha'
# Within `spec/spec_helper.rb`
RSpec.configure do |config|
  config.mock_with :mocha
end
Note: There is no need to use a require statement to setup Mocha; RSpec does this itself.
Cucumber
# In e.g. features/support/mocha.rb
require 'mocha/api'
World(Mocha::API)
Around do |scenario, block|
  begin
    mocha_setup
    block.call
    mocha_verify
  ensure
    mocha_teardown
  end
end
Rails
If you're loading Mocha using Bundler within a Rails application, you should setup Mocha manually e.g. at the bottom of your test_helper.rb.
Minitest
Note that since Rails v4 (at least), ActiveSupport::TestCase has inherited from Minitest::Test or its earlier equivalents. Thus unless you are explicitly using Test::Unit, you are likely to be using Minitest.
# Gemfile in Rails app
gem 'mocha'
# At bottom of test_helper.rb (or at least after `require 'rails/test_help'`)
require 'mocha/minitest'
Other Test Framework
Follow the instructions for the relevant test framework in the Bundler section, but ensure that the relevant Mocha file (mocha/minitest, mocha/test_unit, or mocha/api) is required after the test framework has been loaded, e.g. at the bottom of test_helper.rb or spec_helper.rb, or at least after rails/test_help has been required.
Known Issues
- Prior to v1.15.0 (when support for Ruby v1.8 was dropped), stubbing an aliased class method where the original method is defined in a module that's used to extendthe class doesn't work in Ruby v1.8. Seetest/acceptance/stub_method_defined_on_module_and_aliased_test.rbfor an example of this behaviour.
Usage
Quick Start
require 'test/unit'
require 'mocha/test_unit'
class MiscExampleTest < Test::Unit::TestCase
  def test_mocking_a_class_method
    product = Product.new
    Product.expects(:find).with(1).returns(product)
    assert_equal product, Product.find(1)
  end
  def test_mocking_an_instance_method_on_a_real_object
    product = Product.new
    product.expects(:save).returns(true)
    assert product.save
  end
  def test_stubbing_instance_methods_on_real_objects
    prices = [stub(pence: 1000), stub(pence: 2000)]
    product = Product.new
    product.stubs(:prices).returns(prices)
    assert_equal [1000, 2000], product.prices.collect {|p| p.pence}
  end
  def test_stubbing_an_instance_method_on_all_instances_of_a_class
    Product.any_instance.stubs(:name).returns('stubbed_name')
    product = Product.new
    assert_equal 'stubbed_name', product.name
  end
  def test_traditional_mocking
    object = mock('object')
    object.expects(:expected_method).with(:p1, :p2).returns(:result)
    assert_equal :result, object.expected_method(:p1, :p2)
  end
  def test_shortcuts
    object = stub(method1: :result1, method2: :result2)
    assert_equal :result1, object.method1
    assert_equal :result2, object.method2
  end
end
Mock Objects
class Enterprise
  def initialize(dilithium)
    @dilithium = dilithium
  end
  def go(warp_factor)
    warp_factor.times { @dilithium.nuke(:anti_matter) }
  end
end
require 'test/unit'
require 'mocha/test_unit'
class EnterpriseTest < Test::Unit::TestCase
  def test_should_boldly_go
    dilithium = mock()
    dilithium.expects(:nuke).with(:anti_matter).at_least_once  # auto-verified at end of test
    enterprise = Enterprise.new(dilithium)
    enterprise.go(2)
  end
end
Partial Mocking
class Order
  attr_accessor :shipped_on
  def total_cost
    line_items.inject(0) { |total, line_item| total + line_item.price } + shipping_cost
  end
  def total_weight
    line_items.inject(0) { |total, line_item| total + line_item.weight }
  end
  def shipping_cost
    total_weight * 5 + 10
  end
  class << self
    def find_all
      # Database.connection.execute('select * from orders...
    end
    def number_shipped_since(date)
      find_all.select { |order| order.shipped_on > date }.length
    end
    def unshipped_value
      find_all.inject(0) { |total, order| order.shipped_on ? total : total + order.total_cost }
    end
  end
end
require 'test/unit'
require 'mocha/test_unit'
class OrderTest < Test::Unit::TestCase
  # illustrates stubbing instance method
  def test_should_calculate_shipping_cost_based_on_total_weight
    order = Order.new
    order.stubs(:total_weight).returns(10)
    assert_equal 60, order.shipping_cost
  end
  # illustrates stubbing class method
  def test_should_count_number_of_orders_shipped_after_specified_date
    now = Time.now; week_in_secs = 7 * 24 * 60 * 60
    order_1 = Order.new; order_1.shipped_on = now - 1 * week_in_secs
    order_2 = Order.new; order_2.shipped_on = now - 3 * week_in_secs
    Order.stubs(:find_all).returns([order_1, order_2])
    assert_equal 1, Order.number_shipped_since(now - 2 * week_in_secs)
  end
  # illustrates stubbing instance method for all instances of a class
  def test_should_calculate_value_of_unshipped_orders
    Order.stubs(:find_all).returns([Order.new, Order.new, Order.new])
    Order.any_instance.stubs(:shipped_on).returns(nil)
    Order.any_instance.stubs(:total_cost).returns(10)
    assert_equal 30, Order.unshipped_value
  end
end
Thread safety
Mocha currently does not attempt to be thread-safe.
Can I test multi-threaded code with Mocha?
The short answer is no. In multi-threaded code Mocha exceptions may be raised in a thread other than the one which is running the test and thus a Mocha exception may not be correctly intercepted by Mocha exception handling code.
Can I run my tests across multiple threads?
Maybe, but probably not. Partial mocking changes the state of objects in the ObjectSpace which is shared across all threads in the Ruby process and this access to what is effectively global state is not synchronized. So, for example, if two tests are running concurrently and one uses #any_instance to modify a class, both tests will see those changes immediately.
Expectation matching / invocation order
Stubs and expectations are basically the same thing. A stub is just an expectation of zero or more invocations. The Expectation#stubs method is syntactic sugar to make the intent of the test more explicit.
When a method is invoked on a mock object, the mock object searches through its expectations from newest to oldest to find one that matches the invocation. After the invocation, the matching expectation might stop matching further invocations. If the expectation that matches the invocation has a cardinality of "never", then an unexpected invocation error is reported.
See the documentation for Mocha::Mock for further details.
Configuration
If you want, Mocha can generate a warning or raise an exception when:
- stubbing a method unnecessarily
- stubbing method on a non-mock object
- stubbing a non-existent method
- stubbing a non-public method
See the documentation for Mocha::Configuration for further details.
MOCHA_OPTIONS
MOCHA_OPTIONS is an environment variable whose value can be set to a comma-separated list, so that we can specify multiple options e.g. MOCHA_OPTIONS=debug,use_test_unit_gem.
Only the following values are currently recognized and have an effect:
- debug: Enables a debug mode which will output backtraces for each deprecation warning. This is useful for finding where in the test suite the deprecated calls are.
Semantic versioning
- Every effort is made to comply with semantic versioning.
- However, this only applies to the behaviour documented in the public API.
- The documented public API does not include the content or format of messsages displayed to the user, e.g. assertion failure messages.
Useful Links
- Official Documentation
- Source Code
- Mailing List
- James Mead's Blog
- An Introduction To Mock Objects In Ruby
- Mocks Aren't Stubs
- Growing Object-Oriented Software Guided By Tests
- Mock Roles Not Objects
- jMock
Contributors
See this list of contributors.
Releasing a new version
- Update the RELEASE.md file with a summary of changes
- Bump the version in lib/mocha/version.rb
- Commit & push to GitHub
- Check CircleCI build is passing - https://app.circleci.com/pipelines/github/freerange/mocha 
- Generate documentation: 
$ MOCHA_GENERATE_DOCS=true bundle install
$ MOCHA_GENERATE_DOCS=true rake generate_docs
- Commit documentation & push to GitHub
- Sign in to rubygems.org and find API key - https://rubygems.org/profile/edit
$ curl -u <email-address> -H 'OTP:<one-time-password>' https://rubygems.org/api/v1/api_key.yaml > ~/.gem/credentials; chmod 0600 ~/.gem/credentials
- Release gem to Rubygems:
$ rake release
[runs tests]
mocha 1.2.0 built to pkg/mocha-1.2.0.gem.
Tagged v1.2.0.
Pushed git commits and tags.
Pushed mocha 1.2.0 to rubygems.org.
History
Mocha was initially harvested from projects at Reevoo. It's syntax is heavily based on that of jMock.
License
© Copyright James Mead 2006
You may use, copy and redistribute this library under the same terms as Ruby itself or under the MIT license.