require 'rspec/mocks/framework' require 'rspec/mocks/extensions/object' require 'rspec/mocks/version' module Rspec # == Mocks and Stubs # # RSpec will create Mock Objects and Stubs for you at runtime, or attach stub/mock behaviour # to any of your real objects (Partial Mock/Stub). Because the underlying implementation # for mocks and stubs is the same, you can intermingle mock and stub # behaviour in either dynamically generated mocks or your pre-existing classes. # There is a semantic difference in how they are created, however, # which can help clarify the role it is playing within a given spec. # # == Mock Objects # # Mocks are objects that allow you to set and verify expectations that they will # receive specific messages during run time. They are very useful for specifying how the subject of # the spec interacts with its collaborators. This approach is widely known as "interaction # testing". # # Mocks are also very powerful as a design tool. As you are # driving the implementation of a given class, Mocks provide an anonymous # collaborator that can change in behaviour as quickly as you can write an expectation in your # spec. This flexibility allows you to design the interface of a collaborator that often # does not yet exist. As the shape of the class being specified becomes more clear, so do the # requirements for its collaborators - often leading to the discovery of new types that are # needed in your system. # # Read Endo-Testing[http://www.mockobjects.com/files/endotesting.pdf] for a much # more in depth description of this process. # # == Stubs # # Stubs are objects that allow you to set "stub" responses to # messages. As Martin Fowler points out on his site, # mocks_arent_stubs[http://www.martinfowler.com/articles/mocksArentStubs.html]. # Paraphrasing Fowler's paraphrasing # of Gerard Meszaros: Stubs provide canned responses to messages they might receive in a test, while # mocks allow you to specify and, subsquently, verify that certain messages should be received during # the execution of a test. # # == Partial Mocks/Stubs # # RSpec also supports partial mocking/stubbing, allowing you to add stub/mock behaviour # to instances of your existing classes. This is generally # something to be avoided, because changes to the class can have ripple effects on # seemingly unrelated specs. When specs fail due to these ripple effects, the fact # that some methods are being mocked can make it difficult to understand why a # failure is occurring. # # That said, partials do allow you to expect and # verify interactions with class methods such as +#find+ and +#create+ # on Ruby on Rails model classes. # # == Further Reading # # There are many different viewpoints about the meaning of mocks and stubs. If you are interested # in learning more, here is some recommended reading: # # * Mock Objects: http://www.mockobjects.com/ # * Endo-Testing: http://www.mockobjects.com/files/endotesting.pdf # * Mock Roles, Not Objects: http://www.mockobjects.com/files/mockrolesnotobjects.pdf # * Test Double Patterns: http://xunitpatterns.com/Test%20Double%20Patterns.html # * Mocks aren't stubs: http://www.martinfowler.com/articles/mocksArentStubs.html # # == Creating a Mock # # You can create a mock in any specification (or setup) using: # # double(name, options={}) # # The optional +options+ argument is a +Hash+. Currently the only supported # option is +:null_object+. Setting this to true instructs the mock to ignore # any messages it hasn’t been told to expect – and quietly return itself. For example: # # double("person", :null_object => true) # # == Creating a Stub # # You can create a stub in any specification (or setup) using: # # stub(name, stub_methods_and_values_hash) # # For example, if you wanted to create an object that always returns # "More?!?!?!" to "please_sir_may_i_have_some_more" you would do this: # # stub("Mr Sykes", :please_sir_may_i_have_some_more => "More?!?!?!") # # == Creating a Partial Mock # # You don't really "create" a partial mock, you simply add method stubs and/or # mock expectations to existing classes and objects: # # Factory.should_receive(:find).with(id).and_return(value) # obj.stub(:to_i).and_return(3) # etc ... # # == Expecting Messages # # my_mock.should_receive(:sym) # my_mock.should_not_receive(:sym) # # == Expecting Arguments # # my_mock.should_receive(:sym).with(*args) # my_mock.should_not_receive(:sym).with(*args) # # == Argument Matchers # # Arguments that are passed to #with are compared with actual arguments received # using == by default. In cases in which you want to specify things about the arguments # rather than the arguments themselves, you can use any of RSpec's Expression Matchers. # They don't all make syntactic sense (they were primarily designed for use with # Rspec::Expectations), but you are free to create your own custom Rspec::Matchers. # # Rspec::Mocks does provide one additional Matcher method named #ducktype. # # In addition, Rspec::Mocks adds some keyword Symbols that you can use to # specify certain kinds of arguments: # # my_mock.should_receive(:sym).with(no_args()) # my_mock.should_receive(:sym).with(any_args()) # my_mock.should_receive(:sym).with(1, kind_of(Numeric), "b") #2nd argument can any kind of Numeric # my_mock.should_receive(:sym).with(1, boolean(), "b") #2nd argument can true or false # my_mock.should_receive(:sym).with(1, /abc/, "b") #2nd argument can be any String matching the submitted Regexp # my_mock.should_receive(:sym).with(1, anything(), "b") #2nd argument can be anything at all # my_mock.should_receive(:sym).with(1, ducktype(:abs, :div), "b") # #2nd argument can be object that responds to #abs and #div # # == Receive Counts # # my_mock.should_receive(:sym).once # my_mock.should_receive(:sym).twice # my_mock.should_receive(:sym).exactly(n).times # my_mock.should_receive(:sym).at_least(:once) # my_mock.should_receive(:sym).at_least(:twice) # my_mock.should_receive(:sym).at_least(n).times # my_mock.should_receive(:sym).at_most(:once) # my_mock.should_receive(:sym).at_most(:twice) # my_mock.should_receive(:sym).at_most(n).times # my_mock.should_receive(:sym).any_number_of_times # # == Ordering # # my_mock.should_receive(:sym).ordered # my_mock.should_receive(:other_sym).ordered # #This will fail if the messages are received out of order # # == Setting Reponses # # Whether you are setting a mock expectation or a simple stub, you can tell the # object precisely how to respond: # # my_mock.should_receive(:sym).and_return(value) # my_mock.should_receive(:sym).exactly(3).times.and_return(value1, value2, value3) # # returns value1 the first time, value2 the second, etc # my_mock.should_receive(:sym).and_return { ... } #returns value returned by the block # my_mock.should_receive(:sym).and_raise(error) # #error can be an instantiated object or a class # #if it is a class, it must be instantiable with no args # my_mock.should_receive(:sym).and_throw(:sym) # my_mock.should_receive(:sym).and_yield(values,to,yield) # my_mock.should_receive(:sym).and_yield(values,to,yield).and_yield(some,other,values,this,time) # # for methods that yield to a block multiple times # # Any of these responses can be applied to a stub as well, but stubs do # not support any qualifiers about the message received (i.e. you can't specify arguments # or receive counts): # # my_mock.stub(:sym).and_return(value) # my_mock.stub(:sym).and_return(value1, value2, value3) # my_mock.stub(:sym).and_raise(error) # my_mock.stub(:sym).and_throw(:sym) # my_mock.stub(:sym).and_yield(values,to,yield) # my_mock.stub(:sym).and_yield(values,to,yield).and_yield(some,other,values,this,time) # # == Arbitrary Handling # # Once in a while you'll find that the available expectations don't solve the # particular problem you are trying to solve. Imagine that you expect the message # to come with an Array argument that has a specific length, but you don't care # what is in it. You could do this: # # my_mock.should_receive(:sym) do |arg| # arg.should be_an_istance_of(Array) # arg.length.should == 7 # end # # Note that this would fail if the number of arguments received was different from # the number of block arguments (in this case 1). # # == Combining Expectation Details # # Combining the message name with specific arguments, receive counts and responses # you can get quite a bit of detail in your expectations: # # my_mock.should_receive(:<<).with("illegal value").once.and_raise(ArgumentError) module Mocks end end