Verify login functionality runs correctly in parallel tests on CI

Preconditions (3)

Step 1: Open the login page URL in a browser

Step 2: Enter 'user1@example.com' in the email field

Step 3: Enter 'Password1!' in the password field

Step 4: Click the login button

Step 5: Verify the user is redirected to the dashboard page

Step 6: Repeat the above steps simultaneously with 'user2@example.com' and 'user3@example.com' credentials in separate test threads

✅ Expected Result: All parallel tests complete successfully with each user redirected to their dashboard without interference or errors

Automation Requirements - TestNG with Selenium WebDriver

Assertions Needed:

Verify current URL contains '/dashboard' after login

Verify login button is clickable before clicking

Verify no test interference occurs between parallel threads

Best Practices:

Use TestNG @DataProvider for parallel data-driven tests

Use explicit waits to handle dynamic page elements

Configure TestNG XML to enable parallel test execution

Use thread-safe WebDriver instances for each test thread

Automated Solution

Selenium Java

import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.chrome.ChromeDriver;
import org.openqa.selenium.support.ui.ExpectedConditions;
import org.openqa.selenium.support.ui.WebDriverWait;
import org.testng.Assert;
import org.testng.annotations.AfterMethod;
import org.testng.annotations.BeforeMethod;
import org.testng.annotations.DataProvider;
import org.testng.annotations.Test;

import java.time.Duration;

public class ParallelLoginTest {

    private ThreadLocal<WebDriver> driver = new ThreadLocal<>();

    @BeforeMethod
    public void setUp() {
        // Setup ChromeDriver for each thread
        System.setProperty("webdriver.chrome.driver", "path/to/chromedriver");
        driver.set(new ChromeDriver());
    }

    @Test(dataProvider = "loginData", threadPoolSize = 3)
    public void testLogin(String email, String password) {
        WebDriver webDriver = driver.get();
        webDriver.get("https://example.com/login");

        WebDriverWait wait = new WebDriverWait(webDriver, Duration.ofSeconds(10));

        WebElement emailField = wait.until(ExpectedConditions.elementToBeClickable(By.id("email")));
        emailField.clear();
        emailField.sendKeys(email);

        WebElement passwordField = webDriver.findElement(By.id("password"));
        passwordField.clear();
        passwordField.sendKeys(password);

        WebElement loginButton = wait.until(ExpectedConditions.elementToBeClickable(By.id("loginBtn")));
        loginButton.click();

        // Wait for dashboard URL
        wait.until(ExpectedConditions.urlContains("/dashboard"));

        String currentUrl = webDriver.getCurrentUrl();
        Assert.assertTrue(currentUrl.contains("/dashboard"), "User should be redirected to dashboard");
    }

    @DataProvider(name = "loginData", parallel = true)
    public Object[][] loginData() {
        return new Object[][] {
            {"user1@example.com", "Password1!"},
            {"user2@example.com", "Password2!"},
            {"user3@example.com", "Password3!"}
        };
    }

    @AfterMethod
    public void tearDown() {
        driver.get().quit();
        driver.remove();
    }
}

This test class uses TestNG and Selenium WebDriver to run login tests in parallel.

We use ThreadLocal<WebDriver> to ensure each test thread has its own browser instance, avoiding interference.

The @DataProvider supplies three sets of login credentials and is marked parallel=true to enable parallel execution.

The @Test method uses explicit waits to ensure elements are ready before interacting, improving reliability.

Assertions check that after login, the URL contains '/dashboard', confirming successful login.

Finally, @BeforeMethod and @AfterMethod setup and clean up the WebDriver instances per test thread.

This setup is suitable for running in a CI environment configured to run TestNG tests in parallel.

Common Mistakes - 4 Pitfalls

Using a single WebDriver instance shared across parallel tests

Not using explicit waits before interacting with elements

Hardcoding test data inside test methods instead of using DataProvider

{'mistake': 'Not configuring TestNG XML for parallel execution', 'why_bad': 'Tests will run sequentially, missing the benefit of parallelization in CI.', 'correct_approach': "Configure TestNG suite XML with parallel='methods' or parallel='tests' and thread-count."}

Bonus Challenge

Now add data-driven testing with 3 different user credentials to run in parallel

Show Hint