Behavior-Driven Development (BDD) Automation Testing in Python

In today's software development field, Behavior Driven Development (BDD) as an emerging testing methodology, gradually by more and more developers' attention and favor.Python as a powerful and easy to use programming language, in the implementation of BDD also has a unique advantage. So, how to use Python to achieve BDD automation testing? This article will provide you with a detailed analysis.

How to implement Behavior Driven Development (BDD) automated tests efficiently with Python? What are the tools and methods that can help us apply BDD in real projects?

Behave, a tool that supports behavior-driven development written in python, lowers the technical barrier and facilitates teamwork by writing test cases in natural language. Combined with step definitions and test runners, Behave can be easily integrated into automated testing frameworks to support testing for all types of applications. Whether you are testing web applications, mobile applications or APIs, Behave provides powerful functionality and flexible extensibility, making it a great choice for automation testing!

What is BDD?

Behavior-Driven Development (BDD, Behavior-Driven Development) is a software development process designed to improve the quality of software by encouraging collaboration and communication.The core concept of BDD is to describe the behavior of the software in natural language so that business people, developers, and testers can participate.BDD evolved from Test-Driven Development (TDD, Test-Driven Development), which emphasizes writing tests in terms of business value and user requirements.BDD uses natural language to write test cases that are easier to understand and maintain. BDD is an evolution of Test-Driven Development (TDD), which emphasizes writing tests in terms of business value and user requirements.BDD uses natural language to write test cases that are easier to understand and maintain.

The main components of BDD include:

1. Feature：

Describe a portion of the software's functionality, e.g., user login functionality

2. Scenario：

Describe specific scenarios or use cases in the feature, each containing a series of steps. For example: successful login and failed login

3. Steps：

To describe specific operations and expected results, use the Given-When-Then syntax.

Given user on the login page
When the user enters a valid username and password
Then users should see the home page

Behave: A Cucumber-like BDD Framework for Python

Cucumber is a very popular framework for BDD in the industry, but Cucumber itself doesn't directly support Python, and the Python community has a similar tool calledBehaveIt is a BDD framework designed for Python that functions and is used in a very similar way to Cucumber. It allows you to write test cases in natural language. These test cases are called Feature Files and use a syntax called Gherkin, which is easy to understand and allows non-technical people to participate in writing test cases. It is widely used in automated testing in conjunction with the Behave BDD framework:

Web Application Automation Testing

Use tools like Selenium in conjunction with Behave to automate end-to-end testing of web applications.

Apply automated tests:

Write and run mobile app automation tests using Behave in conjunction with Appium.

3. Interface automation testing:

Use tools such as requests in conjunction with Behave to automate interface testing.

Behave use

1. Install Behave

Install Behave using pip:

pip install behave

2、Installation of automation testing corresponding to the library

For example, web application automation testing selenium:

pip install selenium

3, create a python project, directory structure reference is as follows:

my_bdd_project/
|-- features/
|   |-- steps/
|   |   |-- login_steps.py
|   |-- 
|-- tests/
|   |-- test_runner.py

4. Define the characteristics file

Characterization files are written in Gherkin syntax and are used to describe specific test cases. Scenarios are parts of a feature file, and each scenario contains a series of steps that simulate user behavior and verify expected results. Scenarios are written in Gherkin syntax and typically contain three parts: Given, When, and Then.

For example, creating a file, which reads as follows:

Feature: User login function

  Scenario: Successful Login
    Given the user is on the login page
    When the user enters a valid username and password
    Then the user should see the home page

  Scenario: Login Failed
    Given User is on the login page
    When the user enters an invalid username and password
    Then the user should see an error message

5. Preparation of step definitions

Step definitions are the mapping of Gherkin syntax to specific code implementations, with each step corresponding to a method that contains specific test logic. For example, using thebehave and Selenium to implement the steps in the feature file above:

establishlogin_steps.py file, which reads as follows.

 1 from behave import given, when, then
 2 from selenium import webdriver
 3 from  import By
 4 
 5 @given('Users on the login page')
 6 def step_given_user_on_login_page(context):
 7      = ()
 8     ('/login')
 9 
10 @when('User enters a valid username and password')
11 def step_when_user_enters_valid_credentials(context):
12     .find_element(, 'username').send_keys('valid_username')
13     .find_element(, 'password').send_keys('valid_password')
14     .find_element(, 'submit').click()
15 
16 @then('Users should see the home page')
17 def step_then_user_should_see_home_page(context):
18     assert 'Home' in 
19 
20 @when('User enters invalid username and password')
21 def step_when_user_enters_invalid_credentials(context):
22     .find_element(, 'username').send_keys('invalid_username')
23     .find_element(, 'password').send_keys('invalid_password')
24     .find_element(, 'submit').click()
25 
26 @then('Users should see an error message')
27 def step_then_user_should_see_error_message(context):
28     error_message = .find_element(, 'error').text
29     assert 'Invalid username or password' in error_message

6、Running test

Run it in the project root directorybehave command to perform the test.

 1 PS D:\workspace_pycharm\my_bdd_project> behave
 2 Feature: User login function # features/:1
 3 
 4   Scenario: Successful login       # features/:3
 5     Given Users on the login page      # features/steps/login_steps.py:7
 6     When User enters a valid username and password # features/steps/login_steps.py:14
 7     Then Users should see the home page       # features/steps/login_steps.py:20
 8 
 9   Scenario: Login Failure       # features/:8
10     Given Users on the login page      # features/steps/login_steps.py:7
11     When User enters invalid username and password # features/steps/login_steps.py:24
12     Then Users should see an error message     # features/steps/login_steps.py:30
13 
14 1 feature passed, 0 failed, 0 skipped
15 2 scenarios passed, 0 failed, 0 skipped
16 6 steps passed, 0 failed, 0 skipped, 0 undefined
17 Took 0m13.667s

Or you can create a newtest_runner.pyDocumentation.

import os
import subprocess

def run_behave_tests():
    result = (['behave'], cwd=((__file__), '../features'))

if __name__ == "__main__":
    run_behave_tests()

Execute the command again:

python tests/test_runner.py

Through the introduction of this article, we understand the application of Python in BDD automation testing, from basic concepts to specific implementations to real-world examples, comprehensively covering all aspects of BDD testing. Mastering this knowledge will not only improve your testing skills, but also help to better apply BDD methods in your projects.

BDD is not just a testing methodology, it's a way of thinking. Implement BDD automated testing with Python to make your development process more efficient and reliable.