Behavior-Driven Development

Detailed explanation

Behavior-Driven Development (BDD) is an agile software development technique that encourages collaboration between developers, QA, and non-technical participants in a software project. BDD focuses on defining the behavior of the system, rather than focusing on the implementation details. This behavior is described using simple, human-readable language, making it accessible to everyone involved in the project.

At its core, BDD is about having conversations and creating shared understanding. It helps teams to define "Done" before development even starts. This shared understanding is then formalized into executable specifications, which serve as both documentation and automated tests.

The BDD Process

The BDD process typically involves the following steps:

1. Discovery: The team collaborates to identify and understand the desired behavior of the system. This is often done through workshops or brainstorming sessions.

2. Formulation: The desired behavior is then formalized into user stories or scenarios. These scenarios are written in a specific format, often using the Gherkin language.

3. Automation: The scenarios are then automated using BDD frameworks. These frameworks provide tools for executing the scenarios and verifying that the system behaves as expected.

4. Execution: The automated scenarios are executed as part of the development process. This provides continuous feedback on the system's behavior.

5. Documentation: The scenarios serve as living documentation of the system's behavior.

Gherkin Language

Gherkin is a plain-text language that is used to describe the behavior of the system in a human-readable format. Gherkin scenarios typically follow the "Given-When-Then" structure:

• Given: Describes the initial context or preconditions of the scenario.
• When: Describes the event or action that triggers the behavior.
• Then: Describes the expected outcome or result of the event.

Here's an example of a Gherkin scenario:

Feature: Account Withdrawal
 
  Scenario: Successful withdrawal
    Given the account balance is $100
    And the card is valid
    And the machine contains enough money
    When the account holder requests $20
    Then the ATM should dispense $20
    And the account balance should be $80
    And the card should be returned

This scenario describes the behavior of an ATM when a user attempts to withdraw money. The Given clauses set up the initial context, the When clause describes the action, and the Then clauses describe the expected outcome.

BDD Frameworks

Several BDD frameworks are available for different programming languages. Some popular frameworks include:

• Cucumber: Cucumber is a popular BDD framework that supports multiple programming languages, including Ruby, Java, and JavaScript.
• SpecFlow: SpecFlow is a BDD framework for .NET.
• Behave: Behave is a BDD framework for Python.
• JBehave: JBehave is a BDD framework for Java.

These frameworks provide tools for parsing Gherkin scenarios, executing them, and reporting the results. They also provide mechanisms for mapping the Gherkin steps to code that interacts with the system under test.

Practical Implementation

To implement BDD, you'll need to choose a BDD framework and integrate it into your development workflow. Here's a general outline of the steps involved:

1. Install the BDD framework: Install the framework and any necessary dependencies.

2. Create feature files: Create feature files that contain the Gherkin scenarios. These files should be organized in a way that makes them easy to find and maintain.

3. Implement step definitions: Implement step definitions that map the Gherkin steps to code. These step definitions should interact with the system under test to verify that it behaves as expected.

4. Run the scenarios: Run the scenarios using the BDD framework. The framework will execute the scenarios and report the results.

5. Analyze the results: Analyze the results to identify any failures or errors. Fix any issues and re-run the scenarios to ensure that the system behaves as expected.

Example using Cucumber (Ruby)

Assuming you have Cucumber installed, you would create a feature file (e.g., features/withdrawal.feature) with the Gherkin scenario shown earlier. Then, you would create step definitions (e.g., features/step_definitions/withdrawal_steps.rb) that map the Gherkin steps to Ruby code:

Given("the account balance is ${int}") do |balance|
  @account = Account.new(balance)
end
 
Given("the card is valid") do
  @card = Card.new(valid: true)
end
 
Given("the machine contains enough money") do
  @atm = ATM.new(sufficient_funds: true)
end
 
When("the account holder requests ${int}") do |amount|
  @transaction = @atm.withdraw(@account, amount, @card)
end
 
Then("the ATM should dispense ${int}") do |amount|
  expect(@transaction.dispensed_amount).to eq(amount)
end
 
Then("the account balance should be ${int}") do |balance|
  expect(@account.balance).to eq(balance)
end
 
Then("the card should be returned") do
  expect(@transaction.card_returned).to be true
end

This code defines the behavior of each step in the scenario. When Cucumber runs the scenario, it will execute these step definitions and verify that the system behaves as expected.

Best Practices

• Collaborate with stakeholders: Involve stakeholders in the BDD process to ensure that the scenarios accurately reflect the desired behavior of the system.
• Write clear and concise scenarios: Write scenarios that are easy to understand and maintain.
• Focus on behavior, not implementation: Focus on describing the behavior of the system, rather than the implementation details.
• Use meaningful names: Use meaningful names for scenarios and steps.
• Keep scenarios small: Keep scenarios small and focused on a single behavior.
• Automate scenarios: Automate scenarios to provide continuous feedback on the system's behavior.
• Use BDD as documentation: Treat the scenarios as living documentation of the system's behavior.

Benefits of BDD

• Improved communication: BDD improves communication between developers, QA, and non-technical stakeholders.
• Shared understanding: BDD helps to create a shared understanding of the desired behavior of the system.
• Reduced ambiguity: BDD reduces ambiguity by formalizing the desired behavior into executable specifications.
• Improved test coverage: BDD helps to improve test coverage by ensuring that all aspects of the system's behavior are tested.
• Living documentation: BDD provides living documentation of the system's behavior.

BDD is a powerful technique that can help teams to build better software. By focusing on the behavior of the system and collaborating with stakeholders, teams can create a shared understanding of the desired outcome and deliver software that meets the needs of the users.

Further reading

• Cucumber Documentation: https://cucumber.io/docs/
• SpecFlow Documentation: https://specflow.org/documentation/
• Behave Documentation: https://behave.readthedocs.io/en/latest/
• JBehave Documentation: https://jbehave.org/reference/stable/
• "BDD in Action" by John Ferguson Smart