Behaviour Driven Development (BDD)

BDD is software development process that emerges from test driven development.
BDD combines the general technique of principles of TDD with ideas from Domain Driven Design and Analysis and design to provide software development and management, teams with shared tools and a shared process to collaborate on software development.

BDD is largely faciliated throught the use of a simple domain specific language using natural language constructs that can express the behaviour and the expected outcomes.
BDD is considered an effective technical practice especially when the problem space of the business problem to solve is complex.

Principles of BDD

1. BDD specifies that tests of any unit of software should be specified in terms of the desired behavior of the unit.
2. BDD, also related to how the desired behaviour should be specified.
3. BDD specified business analysis and developer should collaborate and should specify behaviour in terms of user stories.

Scenario/Story:
Returns got stock.

As a:
Store Owner

In order to keep track of stock,
I want to add items back to stock when they're returned.

---

Scenario/Story: Refunded item should be returned to stock.

Given that a customer previously brought a black sweaters from the store.
And I have there 3 black sweaters in stock.
When they return the black sweater for a refund, Then, there should have 4 black sweaters in stock.

Example of BDD

Feature: Login
As a user,
I want to login 
So that, I want to see my todos.

Background: 
    Given the user has browsed to login page


Scenario: Login with correct credentials
    When the user logs with username "thearjun" and password "nepal123"
    Then the user should be redirected to index page

Scenario: Login with incorrect credentials
    When the user logs with username "thearjun" and password "india123"
    Then the error message "Invalid Username or password" should be displayed

Scenario Outline:
    When the user logs with username "<username>" and password "<password>"
    Then the error message "<message>" should be displayed
    Examples:
    | username  | password    | message                      |
    | bishal    | animeislove | Invalid Username or password |
    |           | nepal123    | Invalid password             |
    | thearjun  |             | Invalid Username or password |
    | @#$%^&    | nepal123    | Invalid Username or password |

Scenario: 
    Given the user logs in with following detatils
    | username | password |
    | thearjun | nepal123 |
    Then the user should be redirected to index page