fakes

This is a really simple library to aid in AAA style testing. The primary driver for using this is to be able to make assertions on method calls to collaborators in actual assertions and not as part of setup. It is meant to be used to complement the current testing framework that you are using to aid in the creation of interaction based tests.

Here is a simple example

```ruby class SomeClass def initialize(collaborator) @collaborator = collaborator end def run() @collaborator.send_message(“Hi”) end end

describe SomeClass do context “when run” do let(:collaborator)Fakes#fake let(:sut)SomeClass.new(collaborator)

before(:each) do sut.run end

it “should trigger its collaborator with the correct message” do collaborator.received(:send_message).called_with(“Hi”).should_not be_nil end end end ```

Creating a new fake

To create a new fake, simply leverage the fake method that is mixed into the Kernel module.

```ruby require ‘fakes’

item = fake ```

Specifying the behaviour of a fake

When scaffolding fake return values, the library behaves almost identically to the way RSpec stubs work.

Setup a method to return a value for a particular set of arguments

```ruby collaborator = fake

collaborator.stub(:name_of_method).with(arg1,arg2,arg3).and_return(return_value) ```

Setup a method to return a value regardless of the arguments it is called with

```ruby collaborator = fake

long handed way

collaborator.stub(:name_of_method).ignore_arg.and_return(return_value)

preferred way

collaborator.stub(:name_of_method).and_return(return_value) ```

Setup different return values for different argument sets

```ruby collaborator = fake

Setup a return value for 1

collaborator.stub(:method).with(1).and_return(first_return_value)

Setup a return value for 2

collaborator.stub(:method).with(2).and_return(second_return_value)

Setup a return value when called with everything else

#if you are going to use this, make sure it is used after #setting up return values for specific arguments collaborator.stub(:method).and_return(value_to_return_with_arguments_other_than_1_and_2)

Setup a return value for any number greater than 2 - this makes use of the argument matching syntax described here

collaborator.stub(:method).with(arg_match.greater_than(2)).and_return(second_return_value) ```

Verifying calls made to the fake

Verifying when a call was made

The primary purpose of the library is to help you in doing interaction style testing in a AAA style. Assume the following class is one you would like to test:

```ruby class ItemToTest def initialize(collaborator) @collaborator = collaborator end

def run @collaborator.send_message(“Hello World”) end end ```

ItemToTest is supposed to leverage its collaborator and calls its send_message method with the argument “Hello World”. To verify this using AAA style, interaction testing you can do the following (I am using rspec, but you can use this with any testing library you wish):

```ruby describe ItemToTest do context “when run” do let(:collaborator)Fakes#fake let(:sut)ItemToTest.new(collaborator)

#I typically use a before block to specifically trigger the method that I am testing, so it cleanly #separates it from the assertions I will make later before(:each) do sut.run end

it “should trigger its collaborator with the correct message” do collaborator.received(:send_message).called_with(“Hello World”).should_not be_nil end end end ``` From the example above, you can see that we created the fake and did not need to scaffold it with any behaviour.

ruby let(:collaborator){fake}

You can also see that we are create our System Under Test (sut) and provide it the collaborator:

ruby let(:sut){ItemToTest.new(collaborator)}

We then proceed to invoke the method on the component we are testing

ruby before(:each) do sut.run end

Last but not least, we verify that our collaborator was invoked and with the right arguments:

ruby it "should trigger its collaborator with the correct message" do collaborator.received(:send_message).called_with("Hello World").should_not be_nil end

The nice thing is we can make the assertions after the fact, as opposed to needing to do them as part of setup, which I find is a much more natural way to read things, when you need to do this style of test. Notice that the called_with method return a method_invocation that will be nil if the call was not received. My recommendation would be to use the fakes-rspec library (if you are using rspec) which gives you access to a predefined matcher that you can use as follows:

ruby collaborator.received(:send_message).called_with("Hello World").should_not be_nil

Can be done in fakes-rspec by doing this:

ruby collaborator.should have_received(:send_message,"Hello World")

Verifying that a call should not have been made

Verifying that a call was not made can be done with or without arguments:

```ruby class FirstCollaborator def send_message(message) end end class SecondCollaborator def send_message(message) end end

class SomeItem def initialize @first = FirstCollaborator.new @second = SecondCollaborator.new end

def first_behaviour @first.send_message(“Hello”) end

def second_behaviour @second.send_message(“World”) end end

describe SomeItem do context “when run” do let(:first)Fakes#fake let(:second)Fakes#fake

before(:each) do FirstCollaborator.stub(:new).and_return(first) SecondCollaborator.stub(:new).and_return(second) @sut = SomeItem.new end

before(:each) do @sut.first_behaviour end

it “should trigger its collaborator with the correct message” do first.should have_received(:send_message,”Hello”) end

it “should not trigger its second collaborator” do #again, here would be another option to use a convienience test utility method second.never_received?(:send_message).should be_true #with fakes-rspec it looks like this second.should_not have_received(:send_message) end end end ```

As you can see, in this test we want to verify that one collaborator was triggered and the other not. If you cared about specifying arguments it should not have been called with, you can do the same as a regular verification.