About ===== Handrolling mocks is the best, but involves more overhead than necessary, and usually has less helpful error messages. Surrogate addresses this by endowing your objects with common things that most mocks need. Currently it is only integrated with RSpec. Features ======== * Declarative syntax * Support default values * Easily override values * RSpec matchers for asserting what happend (what was invoked, with what args, how many times) * RSpec matchers for asserting the Mock's interface matches the real object * Support for exceptions * Queue return values * Initialization information is always recorded Usage ===== **Endow** a class with surrogate abilities ```ruby class Mock Surrogate.endow self end ``` Define a **class method** by using `define` in the block when endowing your class. ```ruby class MockClient Surrogate.endow self do define(:default_url) { 'http://example.com' } end end MockClient.default_url # => "http://example.com" ``` Define an **instance method** by using `define` outside the block after endowing your class. ```ruby class MockClient Surrogate.endow self define(:request) { ['result1', 'result2'] } end MockClient.new.request # => ["result1", "result2"] ``` If you care about the **arguments**, your block can receive them. ```ruby class MockClient Surrogate.endow self define(:request) { |limit| limit.times.map { |i| "result#{i.next}" } } end MockClient.new.request 3 # => ["result1", "result2", "result3"] ``` You don't need a **default if you set the ivar** of the same name (replace `?` with `_p` for predicates, since you can't have question marks in ivar names) ```ruby class MockClient Surrogate.endow self define(:initialize) { |id| @id, @connected_p = id, true } define :id define :connected? end MockClient.new(12).id # => 12 ``` **Override defaults** with `will_` and `will_have_` ```ruby class MockMP3 Surrogate.endow self define :play # defaults are optional, will raise error if invoked without being told what to do define :info end mp3 = MockMP3.new # verbs mp3.will_play true mp3.play # => true # nouns mp3.will_have_info artist: 'Symphony of Science', title: 'Children of Africa' mp3.info # => {:artist=>"Symphony of Science", :title=>"Children of Africa"} ``` **Errors** get raised ```ruby class MockClient Surrogate.endow self define :request end client = MockClient.new client.will_have_request StandardError.new('Remote service unavailable') begin client.request rescue StandardError => e e # => # end ``` **Queue** up return values ```ruby class MockPlayer Surrogate.endow self define(:move) { 20 } end player = MockPlayer.new player.will_move 1, 9, 3 player.move # => 1 player.move # => 9 player.move # => 3 # then back to default behaviour (or error if none provided) player.move # => 20 ``` You can define **initialize** ```ruby class MockUser Surrogate.endow self do define(:find) { |id| new id } end define(:initialize) { |id| @id = id } define(:id) { @id } end user = MockUser.find 12 user.id # => 12 ``` RSpec Integration ================= Currently only integrated with RSpec, since that's what I use. It has some builtin matchers for querying what happened. Load the RSpec matchers. ```ruby require 'surrogate/rspec' ``` Nouns ----- Given this mock and assuming the following examples happen within a spec ```ruby class MockMP3 Surrogate.endow self define(:info) { 'some info' } end ``` Check if **was invoked** with `have_been_asked_for_its` ```ruby mp3.should_not have_been_asked_for_its :info mp3.info mp3.should have_been_asked_for_its :info ``` Invocation **cardinality** by chaining `times(n)` ```ruby mp3.info mp3.info mp3.should have_been_asked_for_its(:info).times(2) ``` Invocation **arguments** by chaining `with(args)` ```ruby mp3.info :title mp3.should have_been_asked_for_its(:info).with(:title) ``` Supports RSpec's `no_args` matcher (the others coming in future versions) ```ruby mp3.info mp3.should have_been_asked_for_its(:info).with(no_args) ``` Cardinality of a specific set of args `with(args)` and `times(n)` ```ruby mp3.info :title mp3.info :title mp3.info :artist mp3.should have_been_asked_for_its(:info).with(:title).times(2) mp3.should have_been_asked_for_its(:info).with(:artist).times(1) ``` Verbs ----- Given this mock and assuming the following examples happen within a spec ```ruby class MockMP3 Surrogate.endow self define(:play) { true } end ``` Check if **was invoked** with `have_been_told_to` ```ruby mp3.should_not have_been_told_to :play mp3.play mp3.should have_been_told_to :play ``` Also supports the same `with(args)` and `times(n)` that nouns have. Initialization -------------- Query with `have_been_initialized_with`, which is exactly the same as saying `have_been_told_to(:initialize).with(...)` ```ruby class MockUser Surrogate.endow self define(:initialize) { |id| @id = id } define :id end user = MockUser.new 12 user.id.should == 12 user.should have_been_initialized_with 12 ``` Substitutability ---------------- After you've implemented the real version of your mock (assuming a [top-down](http://vimeo.com/31267109) style of development), how do you prevent your real object from getting out of synch with your mock? Assert that your mock has the **same interface** as your real class. This will fail if the mock inherits methods methods not on the real class. And it will fail if the real class has or lacks any methods defined on the mock or inherited by the mock. Presently, it will ignore methods defined directly in the mock (as it adds quite a few of its own methods, and generally considers them to be helpers). In a future version, you will be able to tell it to treat other methods as part of the API (will fail if they don't match, and maybe record their values). ```ruby class User def initialize(id)end def id()end end class MockUser Surrogate.endow self define(:initialize) { |id| @id = id } define :id end # they are the same MockUser.should substitute_for User # mock has extra method MockUser.define :name MockUser.should_not substitute_for User # the same again via inheritance class UserWithName < User def name()end end MockUser.should substitute_for UserWithName # real class has extra methods class UserWithNameAndAddress < UserWithName def address()end end MockUser.should_not substitute_for UserWithNameAndAddress ``` Sometimes you don't want to have to implement the entire interface. In these cases, you can assert that the methods on the mock are a **subset** of the methods on the real class. ```ruby class User def initialize(id)end def id()end def name()end end class MockUser Surrogate.endow self define(:initialize) { |id| @id = id } define :id end # doesn't matter that real user has a name as long as it has initialize and id MockUser.should substitute_for User, subset: true # but now it fails b/c it has no address MockUser.define :address MockUser.should_not substitute_for User, subset: true ``` How do I introduce my mocks? ============================ This is known as dependency injection. There are many ways you can do this, you can pass the object into the initializer, you can pass a factory to your class, you can give the class that depends on the mock a setter and then override it whenever you feel it is necessary, you can use RSpec's `#stub` method to put it into place. Personally, I use [Deject](https://rubygems.org/gems/deject), another gem I wrote. For more on why I feel it is a better solution than the above methods, see it's [readme](https://github.com/JoshCheek/deject/tree/938edc985c65358c074a7c7b7bbf18dc11e9450e#why-write-this). But why write this? =================== Need to put an explanation here soon. In the meantime, I wrote a [blog](http://blog.8thlight.com/josh-cheek/2011/11/28/three-reasons-to-roll-your-own-mocks.html) that touches on the reasons. Special Thanks ============== * [Kyle Hargraves](https://github.com/pd) for changing the name of his internal gem so that I could take Surrogate * [David Chelimsky](http://blog.davidchelimsky.net/) for pairing with me to make Surrogate integrate better with RSpec * [Corey Haines](http://coreyhaines.com/) for pairing on substitutability with me * [Enova](http://www.enovafinancial.com/) for giving me time and motivation to work on this during Enova Labs. * [8th Light](http://8thlight.com/) for giving me time to work on this during our weekly Wazas, and the general encouragement and interest TODO ---- * Add a better explanation for motivations * Figure out whether I'm supposed to be using clone or dup for the object -.^ (looks like there may also be an `initialize_copy` method I can take advantage of instead of crazy stupid shit I'm doing now) * don't blow up when delegating to the Object#initialize with args * queues should not reset when done, they should raise Future Features --------------- * have some sort of reinitialization that can hook into setup/teardown steps of test suite * Support arity checking as part of substitutability * Support for blocks * Ability to disassociate the method name from the test (e.g. you shouldn't need to change a test just because you change a name) * declare normal methods as being part of the API (e.g. for inheritance) * assertions for order of invocations & methods * class generator? (supports a top-down style of development for when you write your mocks before you write your implementations) * extract surrogate/rspec into its own gem? * deal with hard dependency on rspec-mocks * support subset-substitutabilty not being able to touch real methods (e.g. #respond_to?)