Category Archives: Behaviour Driven Development

Specifying raising of errors in RSpec

RSpec allows a developer to specify that an error is raised within a block with the raise_error method. It’s a nice expressive way of saying that your code should fail when it needs to.

But my tiny brain has often been confused with using it at times, more so when the error class requires parameters for instantiation and when used in conjunction with the and_raise method on a stub or a mock

Consider the snippet below where my Widget depends on Thingamajig to do its funky thing in order to run. But Thingamajig is rigged to explode in a mass of funkyness and make Widget all useless.

describe Widget do
it "should re-raise errors as a Widget::UnrecoverableError" do
# expectations
thingamajig = stub(Thingamajig)
thingamajig.should_receive(:do_funky_thing).and_raise(Thingamajig::FunkyExplosion.new('The funky thang exploded yo'))

# our SUT
widget = Widget.new(thingamajig)

#verification
lambda { widget.run }.should raise_error(Widget::UnrecoverableError, 'The funky thang exploded yo')
end
end

Do you notice the inconsistency between the way errors are declared in the expectation and the actual verification?

# expectations
thingamajig.should_receive(:do_funky_thing).and_raise(Thingamajig::FunkyThingExplosion.new('The funky thang exploded yo'))

#verification
lambda { widget.run }.should raise_error(Widget::UnrecoverableError, 'The funky thang exploded yo')

The expectation on the stub, ‘thingmajig’ needs the exception instantiated first while verification requires the class name and parameters used to instantiate the error instance.

And no, doing it like this doesn’t work as expected:

lambda { widget.run }.should raise_error(Widget::UnrecoverableError.new('The funky thang exploded yo'))

It’s an unfortunate impedance mismatch that might be caused due to the way Ruby handles the raising of errors.

Advertisements

Behaviour Driven Development != Testing

Testing: Executing a program with the specific intent of uncovering errors.

Software Engineering: A Practitioner’s Approach – Roger S Pressman

The definition of testing by Pressman states that the purpose of performing software testing is to detect errors in a program. This encompasses a wide range of techniques such as black box/white box testing, basis path testing, fault based testing and at a more thorough level, control structure testing.

So where do the specifications in Behaviour Driven Development (BDD) fit into the picture? In this respect, BDD isn’t about testing at all. We write specifications to say that the software exhibits a specific behaviour when its in a certain state. The specifications serve to reinforce the notion that the program is working as expected under known conditions.

Having 100% coverage for code certainly does not mean that a program is free of errors, there are still edge cases that may be too difficult or complex to replicate with an automated test suite. Traditional QA testing is still very much relevant to software projects with BDD employed religiously throughout development.

This has been discussed at length before but it bears repeating: BDD is a design technique that gives you executable documentation of what functions the software is expected to provide.

Using Factories for Rails Fixtures and Test Doubles

Chris Wanstrath has written about making Rails fixtures less painful than they need to be with the FixtureScenarios plugin. Personally, I prefer the Factory approach, nicely explained by Daniel Manges.

I’ve been using factory methods to create in-database ActiveRecord objects for a project that I’ve been working on in Bezurk. Reading Daniel’s article gave me a few ideas on improving the way I create fixtures and mocks. Since I’ve been using RSpec extensively in this project, I’ll present the examples in RSpec.

As the models evolve with the design and its behaviour change accordingly, there is a need to go through all the specifications that create this model and make sure that its created in a valid state. This is more pronounced with the use of test doubles, the test doubles also need to have its method stubs changed to reflect the latest state of the model that its is representing. I happen to make much use of test doubles for test isolation, so trying to manage all these objects became an exercise in patience. As it was getting painful, It’s time to change the way I create these models and test doubles.

As always, a layer of indirection will always go some way to solving a software problem. We introduce a Factory that encapsulates the creation of ActiveRecord objects by providing creation methods.

[ruby]
module FixtureFactory
def create_user(attributes = {})
User.create!(ModelAttributes.user(attributes))
end
end
[/ruby]
We’ll have a Factory for test doubles too.

[ruby]
module MockFactory
def mock_user(method_stubs = {})
mock_model(User, ModelAttributes.user(method_stubs))
end
end
[/ruby]
And the attributes for this model will be declared in a module that’s used by both Factories

[ruby]
module ModelAttributes
def self.user(attributes)
attributes.reverse_merge({:name => ‘doug’})
end
end
[/ruby]

The Factory modules are then included in Spec::Runnner

[ruby]
Spec::Runner.configure do |config|
include FixtureFactory
include MockFactory
end
[/ruby]

The objects can now be created using the factory methods available to all specifications.

[ruby]
doug = create_user
doppelganger = mock_user
[/ruby]

Update
Added links to Chris Wanstrath and Daniel Manges’ articles on managing Rails fixtures.

RSpec your functional tests

The release of RSpec 0.9.4 can be considered a landmark release of sorts. With the inclusion of Spec::Ui 0.2.0, RSpec can now perform functional testing of web applications within a browser. Out of the box support is limited to Watir/Internet Explorer for now as the Selenium RC custom matchers are not implemented yet. includes WATIR/Windows and Watirsafari/OSX. The custom matchers for Selenium RC are not implemented yet but its certainly possible to use Selenium with Spec::Ui, it just won’t read as nicely compared to WATIR. Spec::Ui also comes with a custom result formatter that packages a screenshot of the browser on spec failure, along with its HTML source in the report.

To use Watirsafari in your functional specs, you’ll need to install the gem for it: gem install watirsafari

spec_helper.rb should be updated to include the snippet below (code lifted from the original release announcement):

[ruby]
Spec::Runner.configure do |config|
config.include Spec::Matchers::Watir
end
[/ruby]

The specification will need before and after blocks like this:
[ruby]
before(:all) do
@browser = Watir::Browser.new
end

after(:each) do
# This is needed to make screenshots work
Spec::Ui::ScreenshotFormatter.browser = @browser
end

after(:all) do
@browser.kill! rescue nil
end
[/ruby]

There are a lot more useful information available in the examples supplied with Spec::Ui. Take a look at the samples to get up and running.

Update
My thanks to Aslak Hellesoy for correcting me on support for WATIR and Selenium.