Why data-driven tests increase coverage in Selenium Python - Test Execution Impact

Test Overview

This test runs a login form check with multiple sets of usernames and passwords. It verifies that the login result matches the expected outcome for each data set. This shows how data-driven tests increase coverage by testing many cases in one test.

Test Code - Selenium

Selenium Python

import unittest
from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC

class TestLoginDataDriven(unittest.TestCase):
    def setUp(self):
        self.driver = webdriver.Chrome()
        self.driver.get('https://example.com/login')

    def test_login_multiple_users(self):
        test_data = [
            {'username': 'user1', 'password': 'pass1', 'expected': 'Welcome user1!'},
            {'username': 'user2', 'password': 'wrongpass', 'expected': 'Invalid credentials'},
            {'username': 'user3', 'password': 'pass3', 'expected': 'Welcome user3!'}
        ]

        for data in test_data:
            username_input = WebDriverWait(self.driver, 10).until(
                EC.presence_of_element_located((By.ID, 'username'))
            )
            password_input = self.driver.find_element(By.ID, 'password')
            login_button = self.driver.find_element(By.ID, 'login-btn')

            username_input.clear()
            username_input.send_keys(data['username'])
            password_input.clear()
            password_input.send_keys(data['password'])
            login_button.click()

            message = WebDriverWait(self.driver, 10).until(
                EC.visibility_of_element_located((By.ID, 'message'))
            ).text

            self.assertEqual(message, data['expected'])

    def tearDown(self):
        self.driver.quit()

if __name__ == '__main__':
    unittest.main()

Execution Trace - 9 Steps

Step	Action	System State	Assertion	Result
1	Test starts and browser opens the login page	Browser shows login page with username, password fields and login button	-	PASS
2	Find username, password input fields and login button	Elements are present and interactable	-	PASS
3	Enter username 'user1' and password 'pass1', then click login	Login form filled and submitted	-	PASS
4	Wait for message element and check text	Message displayed: 'Welcome user1!'	Assert message equals 'Welcome user1!'	PASS
5	Repeat steps 2-4 for username 'user2' and password 'wrongpass'	Login form filled and submitted	-	PASS
6	Wait for message element and check text	Message displayed: 'Invalid credentials'	Assert message equals 'Invalid credentials'	PASS
7	Repeat steps 2-4 for username 'user3' and password 'pass3'	Login form filled and submitted	-	PASS
8	Wait for message element and check text	Message displayed: 'Welcome user3!'	Assert message equals 'Welcome user3!'	PASS
9	Test ends and browser closes	Browser closed	-	PASS

Failure Scenario

Failing Condition: If the message text does not match the expected text for any data set

Execution Trace Quiz - 3 Questions

What does the test verify for each set of username and password?

A The displayed message matches the expected result

B The page URL changes after login

C The login button becomes disabled

D The browser title changes

Key Result

Data-driven tests improve coverage by running the same test steps with different inputs and expected results, catching more cases efficiently.