bdd-testing

name	bdd-testing
description	Implement Behaviour-Driven Development with Gherkin scenarios, step definitions, and living documentation. Outputs feature files, step definitions, scenario organisation, and CI integration.
argument-hint	["language/framework","team structure","existing test coverage","stakeholder involvement"]
allowed-tools	Read, Write, Bash

BDD Testing (Behaviour-Driven Development)

BDD bridges the gap between business stakeholders and technical teams by expressing tests in plain language. Gherkin scenarios are executable specifications — they serve as documentation, acceptance criteria, and automated tests simultaneously. The value is alignment, not just test automation.

Process

1. Three amigos. PM, developer, and tester write scenarios together before development. This surfaces ambiguity early.
2. Write Gherkin scenarios. Given-When-Then format describing behaviour from the user's perspective.
3. Implement step definitions. Map each Gherkin step to code.
4. Run scenarios as tests. Scenarios drive development (TDD-style) and serve as regression tests.
5. Maintain living documentation. Scenarios stay current with the product.

Gherkin Feature Files

# features/checkout.feature

Feature: Order Checkout
  As a customer
  I want to complete my purchase
  So that I receive the items I want

  Background:
    Given I am a logged-in customer
    And my cart contains 2 items totalling $59.98

  Scenario: Successful checkout with valid payment
    When I proceed to checkout
    And I enter valid shipping address "123 Main St, Springfield"
    And I enter valid credit card ending in "4242"
    Then my order should be confirmed
    And I should receive a confirmation email
    And my cart should be empty

  Scenario: Checkout fails with declined card
    When I proceed to checkout
    And I enter valid shipping address "123 Main St, Springfield"
    And I enter declined card ending in "0002"
    Then I should see error "Your card was declined"
    And my cart should remain unchanged
    And no order should be created

  Scenario Outline: Minimum order validation
    Given my cart total is <cart_total>
    When I proceed to checkout
    Then I should <outcome>

    Examples:
      | cart_total | outcome                           |
      | $0.00      | see error "Cart is empty"         |
      | $4.99      | see error "Minimum order is $5"   |
      | $5.00      | be able to proceed                |
      | $500.00    | be able to proceed                |

Step Definitions (Python / pytest-bdd)

# tests/bdd/steps/checkout_steps.py
from pytest_bdd import given, when, then, parsers
import pytest

@pytest.fixture
def context():
    return {}

@given("I am a logged-in customer")
def logged_in_customer(context, api_client):
    token = api_client.login("[e-mail]", "password")
    context["auth_headers"] = {"Authorization": f"Bearer {token}"}

@given(parsers.parse("my cart contains {count:d} items totalling {total}"))
def cart_with_items(context, count, total, api_client):
    context["cart_id"] = api_client.create_test_cart(
        headers=context["auth_headers"],
        item_count=count
    )

@when("I proceed to checkout")
def proceed_to_checkout(context, api_client):
    context["checkout_response"] = api_client.post(
        "/api/v1/checkout/start",
        headers=context["auth_headers"],
        json={"cart_id": context["cart_id"]}
    )

@when(parsers.parse('I enter valid credit card ending in "{last4}"'))
def enter_valid_card(context, last4, api_client):
    context[] = api_client.post(
        ,
        headers=context[],
        json={: , : context[]}
    )


 ():
     context[].status_code == 
    order = context[].json()
     order[] == 
    context[] = order[]


 ():
    emails = email_service.get_sent_emails(to=context[])
     (  e[]  e  emails)


 ():
    response = context.get()  context.get()
     response.status_code  [, ]
     message.strip()  response.json().get(, )

Step Definitions (JavaScript / Cucumber)

// features/step_definitions/checkout.steps.js
const { Given, When, Then } = require('@cucumber/cucumber');
const { expect } = require('@playwright/test');

Given('I am a logged-in customer', async function() {
  await this.page.goto('/login');
  await this.page.fill('[data-testid=email]', '[e-mail]');
  await this.page.fill('[data-testid=password]', 'password');
  await this.page.click('[data-testid=login-btn]');
  await expect(this.page).toHaveURL('/dashboard');
});

When('I proceed to checkout', async function() {
  await this.page.click();
   (.).();
});

(,  () {
   (..()).();
  . =  ..().();
});

Anti-Patterns to Avoid

Anti-Pattern	Problem	Fix
BDD without three amigos	Scenarios written by developers only; miss business perspective	PM + dev + tester write scenarios together
UI-only BDD scenarios	Brittle, slow, expensive to maintain	Prefer API-level steps; use UI only for user-visible behaviour
Overly detailed steps	Given I click the blue button in the top-right corner	Behaviour, not implementation: Given I start a new order
One scenario per edge case	200 scenarios covering the same flow	Scenario outlines for data variations; separate scenarios for behaviour variations
Scenarios not maintained	Living documentation becomes stale	Scenarios run in CI; failing scenarios block merge

10 Rules

1. Three amigos write scenarios before development — not after.
2. Scenarios describe behaviour from the user's perspective — not implementation details.
3. Each scenario tests one behaviour — not a full user journey.
4. Scenario outlines handle data variations — separate scenarios handle different behaviours.
5. Steps are reusable across scenarios — avoid duplicating step logic.
6. Background sets up shared preconditions — not all the context for each scenario.
7. Scenarios run in CI and block merge on failure — they are tests, not documentation.
8. Step definitions are thin — they delegate to existing test infrastructure.
9. Avoid UI automation for BDD where API calls are sufficient — it's faster and more stable.
10. The feature file is the specification — if it's not in Gherkin, it's not specified.