CSC/ECE 517 Fall 2012/ch1b 1w69 mv
Introduction to Behavior-Driven Design and User Stories
Behaviour Driven Design( abbreviated BDD) is a software development methodology which involves incorporating stakeholder’s point of view in the development of the software. The software is implemented by taking into consideration its behavior as described by its stakeholders.
Need for BDD
BDD was developed by [Dan North http://dannorth.net/introducing-bdd/] .BDD comes under agile development. Agile development came into picture to overcome the reasons for software project failure.Some of the reasons for software project failure are:<ref name="video">http://www.youtube.com/watch?v=q_A5kAMygOI
</ref>
- Lack of understanding of user requirements.
- Changing requirements
- Pressure to meet the project deadline.
- Budget and time constraints
- Difficulty in software development and management
- Miscommunication or lack of communication between stakeholders.
Agile development involves stakeholder participation throughout the lifetown of the product. BDD helps achieve this objective of agile development.User stories are written in BDD to describe the feature that is to be implemented.User stories can then be used to write tests to check the behaviour desired by the stakeholder.Test Driven Development approach can then be used to implement the system.
Understanding BDD
In order to reduce miscommunication and increase stakeholder participation, BDD asks questions about behaviour of application before and during development. To communicate effectively with people, it is necessary to use plain english language so that non- technical people can express and understand their requirements clearly.This is achieved by using user stories.The feature identified from the interaction with the customer is represented in 1-3 sentences in everyday language in a user story. In most of the cases user stories are written on “ 3x5 “ index cards. The advantage of using “3x5“ cards is that all the stakeholders can give their opinions without being intimidated.This involves all the customers in the brainstorming session. The compact size of the card allows stakeholders to prioritize the features and change them as required during development.Release dates can also be associated with the cards.<ref name="video" />
Format
The generally accepted format for user stories is as follows:<ref name="video" /><ref name="web">http://www.ryangreenhall.com/articles/bdd-by-example.html
</ref>
As a [role] So that [goal] I want to [task]
Consider a video sharing website where users can upload, stream or download movies.One of the features of this site is that user can upload a movie. The user story for this feature is shown in the image on the right.
After identifying user stories we have to describe scenario.Scenario uses a sequence of steps that describe how the user expects the system to behave.
The format for describing a scenario is as follows:<ref name="video" /><ref name="web" />
Given[situation] When [action] Then [expected result]
For the movie uploading user story described above, the scenario is as follows:<ref name="video" /><ref name="web" />
Given[A movie file] When the user uploads the file Then the movie gets added to the RottenPotatoes database and appears in the list of movies.
Different User perception for the same requirement
The behaviour may be described differently by different users. Consider a library system where once a student rents a book, the system recommends a list of books that the student is likely to rent in the future. Different users of the system will have different perspective about the same feature.Consider the following example.
A student may write the following user story to describe the recommendation feature.
As a student So that I can rent the books in advance I want to see the list of books that users usually rent after reading a particular book
A librarian may write the following user story to describe the recommendation feature.
As a Librarian So that I can maintain an inventory of all the books for which there is demand I want to see the list of books that users usually rent after reading a particular book.
Backlog
The implementation of the entire system will consist of multiple user stories.Backlog is a collection of user stories that are pending. This backlog can be used to prioritize the features to be implemented.
Frameworks for BDD
JBehave and RBehave are the two popular frameworks that support BDD. Consider the movie sharing website described above where users can upload, stream or download movies.
The first step in the BDD approach is to write a story for the feature to be implemented.
Story: Upload Movie As a movie fan I would like to add a movie to Rotten Potatoes Database So that I can share a movie with other fans
The second step is the develop the scenario for the story to be implemented.
Scenario: MovieSharing Given A movie file When the user uploads the file Then the movie gets added to the RottenPotatoes database and appears in the list of movies.
The MovieSharing scenario can be used to check if the functionality has been implemented correctly.
The third step is to map stories to java
- Creating the Scenario
To create an executable scenario we have to import org.jbehave.scenario.Scenario and a create a class to describe the scenario. (All the examples to explain BDD have been written in the JBehave Framework) <ref name="web" />
package com.uploadmovie;
import org.jbehave.scenario.Scenario;
public class MovieSharing extends Scenario {
@SuppressWarnings("unchecked")
public MovieSharing() {
super();
}
}
The above code will not produce any output since till now no steps are defined.
In the given example the MovieSharing class will extend the Scenario class.
- Defining Scenario Steps
To create the scenario steps extend org.jbehave.scenario.steps and define methods for each step in the scenario.<ref name="web" />
package com.uploadmovie.steps;
import org.jbehave.scenario.annotations.Given;
import org.jbehave.scenario.annotations.Then;
import org.jbehave.scenario.annotations.When;
import org.jbehave.scenario.steps.Steps;
public class UploadMovieSteps extends Steps {
@Given("movie $moviefilename")
public void movie(String moviefilename) {
}
@When("the the user uploads the file")
public void movieUploads() {
}
@Then("the movie gets added to the Rotten Potatoes database and appears in the list of movies")
public void themoviewillbedisplayed(String notes) {
}
}
The Given, When and the Then annotations are mapped to the methods that will be called when the scenario is executed. The parameters are depicted using the $ sign. In the above scenario $moviename is a parameter.
- Passing Scenario Instance to the constructor of org.jbeahave.scenario.Scenario <ref name="web" />
package com.uploadmovie;
import org.jbehave.scenario.Scenario;
public class MovieSharing extends Scenario {
@SuppressWarnings("unchecked")
public MovieSharing() {
super(new UploadMovieSteps());
}
}
Here the instance of the UploadMovieSteps class will be passed to the the constructor of org.jbeahave.scenario.Scenario.
If the method for the steps in the scenario are implemented correctly it should give the following output:
Given[A movie file] When the user uploads the file Then the movie gets added to the RottenPotatoes database and appears in the list of movies.
Advantages of BDD and User Stories
- Behaviour Driven Design focuses on customer involvement.Therefore the end product is likely to be according to the expectation of the customer.
- User stories can be used to determine acceptance criteria and evaluate the success of the project.
- User Stories are written in plain english. Therefore customers and end users can understand them easily.
- The compact “3x5” cards facilitate maximum participation. They also help to prioritize the features to be implemented and find the backlog.
- User stories can be used to write tests before coding which can save the trouble of debugging later. <ref name="notes"> https://docs.google.com/file/d/0B-WZbzkEKZrlYTI1OWZjNmItMWM0Mi00Y2IxLWEwYmQtOGFiN2RlYjBjMDRi/edit </ref>
Disadvantages of BDD and User Stories
- It is difficult to maintain continuous contact with the stakeholders.
- It may lead to bad software architecture. <ref name="notes" />
References
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