Behaviour Driven vs Test Driven Development (BDD vs TDD)

What is TDD?

TDD (Test-Driven Development) is a software development approach that relies on writing tests before writing the actual code. TDD is a process where the developer writes an automated test case that defines the expected behaviour of the code and then writes the actual code that passes the test case. TDD is primarily focused on ensuring the code meets the specific requirements of the test cases.

Test cases are written in the format known as Arrange-Act-Assert (AAA). It describes the environment setup, invokes test methods, & verifies the expected output of a feature or function.

Example:

Feature: User Authentication

Arrange: a user with the credentials.
Act: with invoking authentication method.
Assert: on returned result, (success/failure)

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What is BDD?

BDD (Behavior-Driven Development) is a software development approach that extends TDD by placing more emphasis on the behaviour of the system rather than the specific features or requirements.

BDD emphasizes collaboration between developers, testers, Business Analyst & Customer stakeholders to ensure that the system's behaviour is aligned with the business goals. BDD requires that all participants use a common language to describe the behaviour of the system in terms of user stories, acceptance criteria and scenarios.

The scenarios are typically written in a specific format known as Given-When-Then (GWT). It describes the context, action, and expected outcome of a particular feature or function.

Overall, BDD helps to align the development process with business goals and customer needs and ensures that software is developed in a way that meets those requirements.

Example:

Feature: User Authentication

Expected behaviour: As a user, I want to log in to the system so that I can access my account.

Scenario: Valid credentials

Given: a user with valid credentials. 
When: the user logs in with their credentials.
Then: the user is directed to their account page.

Scenario: Invalid credentials

Given: a user with invalid credentials.
When: the user logs in with their credentials.
Then: an error message is displayed.

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TDD implementation

class LoginTests: XCTestCase {
    func testLoginSuccess() {
        // Arrange
        let username = "peter.parker"
        let password = "V@lidPassw0rd"
        let authService = AuthService()

        // Act
        let result = authService.login(username: username, password: password)

        // Assert
        XCTAssertTrue(result.success)
        XCTAssertEqual(result.user.username, username)
    }

    func testLoginFailure() {
        // Arrange
        let username = "peter.parker"
        let password = "inV@lidPassw0rd"
        let authService = AuthService()

        // Act
        let result = authService.login(username: username, password: password)

        // Assert
        XCTAssertFalse(result.success)
        XCTAssertEqual(result.error, .invalidCredentials)
    }
}

BDD Implementation

class LoginScreen {
    var username: String
    var password: String
    func enterUsername(_ username: String) {
        self.username = username
    }

    func enterPassword(_ password: String) {
        self.password = password
    }

    func tapLoginButton() {
        let authService = AuthService()
        authService.login(username: username, password: password)
    }
}

class HomeScreen {
    func isDisplayed() -> Bool {
        return true
    }
}

class LoginTests: XCTestCase {
    func testSuccessfulLogin() {
        // Given
        let loginScreen = LoginScreen()
        let username = "testuser"
        let password = "testpassword"

        // When
        loginScreen.enterUsername(username)
        loginScreen.enterPassword(password)
        loginScreen.tapLoginButton()

        // Then
        let homeScreen = HomeScreen()
        XCTAssertTrue(homeScreen.isDisplayed())
    }
}

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Hope you will start using both BDD & TDD in your daily development routine.

You can reach out to me via Linked In or https://nasirmomin.web.app