A cleaner and DRYer alternative to mocking and stubbing with RSpec
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Not A Mock

A cleaner and DRYer alternative to mocking and stubbing with RSpec.


A Quick Introduction

Mocking (Not)

When you're setting up for a spec, you can ask that method calls on an object be recorded:

object.track_methods(:name, :length)

Once your code has run, you can make assertions about what methods were called, what arguments they took, their results, etc.

object.should have_received(:length).without_args.and_returned(42)
object.should have_received(:name).twice

See NotAMock::Matchers for an explanation of the available assertions, plus Object#track_methods and Object#untrack_methods.


Stubbing Methods

You can replace a method on an object with a stub version like this:

object.stub_method(:method => return_value)

Any call to method after this will return return_value without invoking the method's usual code.

Calls to stub methods are recorded as if you had called track_methods on them, so you can make assertions about them as shown above.

See Object#stub_methods, Object#unstub_methods.

Stubbing Objects

You can also replace an entire object with a stub version like this:

my_object = MyClass.stub_instance(:method_a => return_value, :method_b => return_value, ...)

The returned my_object is a stub instance of MyClass with the given methods defined to provide the corresponding return values.

See Object.stub_instance.

Stubbing ActiveRecord Instances

When you call stub_instance on an ActiveRecord::Base subclass, Not A Mock automatically provides an id method and generates an id for the object.

Yielding To Method Blocks

There are many situation in which a stubbed method will be called with a block attached to it. For example, if you are using the Net-SSH gem, you may have code like this:

Net::SSH.start(@server, @username, :password => @password) do |ssh|

To correctly stub and test the SSH.start method and the ssh.exec! method, you need to yield an object to the block code, that supports a method called “exec!”.

To do this, you can call “yields(*args)” on a stubbed method. For example, you can can stub the SSH.start method and the exec! method, like this:

@sshstub = Net::SSH::Connection::Session.stub_instance(:exec! => nil)

When the .exec! method is called from withing the code block of SSH.start, the @sshstub object will be yielded to the block, allowing you to track the method, provide a stubbed block of code to execute, etc.

In situations where you are calling .yields(*args), you can still provide a stub method block to replace the code that is executed when the stub method is called. There are multiple ways of doing this:

Net::SSH.stub_method(:start).yields(@sshstub) { puts 'this is the method stub code for .start' }


stub_block = lambda { puts 'this is the method stub code for .start' }
Net::SSH.stub_method(:start, &stub_block).yields(@sshstub)

Both of these syntax forms will provide the exact same functionality - the block that puts the string of information will be executed when you call 'Net::SSH.start'


(The following describes using NotAMock with Rails. It should also be possible to use it outside of Rails, but I haven't tried it.)

First, install the rspec and rspec_on_rails plugins:

ruby script/plugin install http://rspec.rubyforge.org/svn/tags/CURRENT/rspec
ruby script/plugin install http://rspec.rubyforge.org/svn/tags/CURRENT/rspec_on_rails
ruby script/generate rspec

(See rspec.info/documentation/rails/install.html for more details.)

Second, install the not_a_mock plugin:

ruby script/plugin install git://github.com/notahat/not_a_mock.git

Finally, add the following to your project's spec/spec_helper.rb:

config.mock_with NotAMock::RspecMockFrameworkAdapter

Installation via Ruby Gems

You can install my extended version of not_a_mock from gemcutter.org with the following steps:

1. gem source -a http://gemcutter.org
2. gem install derickbailey-notamock

Note that you only need to do step 1, once, and you will then be able to install any gem from gemcutter.

If you would like to install the gem from the source, follow these instructions:

1. clone the source code from git://github.com/derickbailey/not_a_mock.git
2. run 'rake jeweler:gemspec' in the root folder of your not_a_mock clone
3. run 'rake jeweler:build' in the root folder of your not_a_mock clone
4. run 'gem install -l pkg/NotAMock-#.#.#.gem' where #.#.# is the version number produced in step 3

After this you will be able to “include 'not_a_mock'” in your rspec tests, and configure rspec as shown for spec_helper.rb, above.


Send bugs, patches, and suggestions to Pete Yandell (pete@notahat.com)

Thanks to Derick Bailey, Pat Allan and Steve Hayes for contributing patches.