describing your systemone specification at a time

Pavneet Singh Saund

t : @pavsaund

l : linkedin.com/in/pavneet

m : pavneet@dolittle.com

w : dolittle.com / blog.dolittle.com

Unit testing

•Accepted fact that we should test our code

•Tests should cover a single unit

•Each Unit should be driven out by a test (Test-Driven Development)

•TDD is meant to help drive out the architecture

Test-Driven Development

• Where to start?

• What to test?

• What NOT to test?

• How much to test?

• How to name your tests?

• Understanding why tests fail?

... but

Behaviour Driven Development

•Term coined by Dan North

•A reaction to confusions and misunderstandings about Test-Driven Development and how it fits in agile processes

•An approach to software development that aids to focus on delivering business value by focus on behaviour

What is BDD?

BDD is a second-generation, outside–in, pull-based, multiple-stakeholder, multiple-scale, high-automation, agile methodology. It describes a cycle of interactions with well-defined outputs, resulting in the delivery of

working, tested software that matters.

- Dan North 2009

BDD is a second-generation, outside–in, pull-based, multiple-stakeholder, multiple-scale, high-automation, agile methodology. It

describes a cycle of interactions with well-defined outputs, resulting in the delivery of working, tested software that matters.

• Based on ideas from :

• Extreme Programming

• Lean Software development

• Domain Driven Design

BDD is a second-generation, outside–in, pull-based, multiple-stakeholder, multiple-scale, high-automation, agile methodology. It

describes a cycle of interactions with well-defined outputs, resulting in the delivery of working, tested software that matters.

• Focusing on specifications that describe the output of the system

• Specifications created Just-in-time and pulled in

BDD is a second-generation, outside–in, pull-based, multiple-stakeholder, multiple-scale, high-automation, agile methodology. It

describes a cycle of interactions with well-defined outputs, resulting in the delivery of working, tested software that matters.

• Not only just a “user”

• Focus on groups of people that are affected by the system

• ex: end-users, business stakeholders, IT-Operations, other developers..

• Defining and using a ubiquitous language for each groups concerns

BDD is a second-generation, outside–in, pull-based, multiple-stakeholder,

multiple-scale, high-automation, agile methodology. It describes a cycle of interactions with well-defined outputs, resulting in the delivery of

working, tested software that matters.

• Specifications can be described at multiple levels

• Top-level can focus on user-interaction

• Further down can focus on affected areas that fulfill the higher levels expectations

• Even lower we can focus on technical implementation, still with a solid focus on the behaviour

Specification by example

•A different way to drive our design (tests)

•Replacing tests with specifications that describe the behaviour of our system

•“Given When Then” - popularized by Gherkin

•Heavy usage of Mocking to abstract away details

What is BDD?

GWT

Given_a_series_of_conditions

When_I_do_something

Then_something_should_happen

//Arrange

//Act

//Assert

MSpec• Context/Specification framework• Uses keywords:

Establish context = () =>Because of = () =>It should = () > •Fluent assertions :

myresult.ShouldEqual(expected_result)•You have to accept the lambda syntax! :)

MSpec practices• “Because of = () => “ should only be one line

• “It_should.. = ()=>” should only contain a single assertion

• Re-use contexts by using multiple level of base classes that each have their own “Establish context = () =>”

• Be consistent with lower_case_naming_of_variables_and_classes - this aids readability

• [Subject()] attribute adds an extra layer of context when “reading” specification ouput in ex. TestDriven.net

• Can also group behaviours with Behaves_like<> to remove duplicated assertions

Typical unit test

Typical mspec specification

DEMO

beware of bugs

• MSpec - https://github.com/machine/machine.specifications

• MSpec with Resharper - https://github.com/machine/machine.specifications#resharper

• Context / Specification - http://www.code-magazine.com/article.aspx?quickid=0805061

• http://en.wikipedia.org/wiki/Behavior-driven_development

• http://dannorth.net/introducing-bdd/

• http://hadihariri.com/2012/04/11/what-bdd-has-taught-me/

• Chirp - Bifrost Sample application with MSpec scenarios http://chirp.dolittle.com / https://github.com/dolittle/chirp/

Resources