Parallel execution configuration in Selenium Java - Build an Automation Script

Configure and run Selenium tests in parallel using TestNG

Preconditions (2)

Step 1: Create a TestNG XML suite file with parallel execution enabled

Step 2: Set parallel attribute to 'tests' and thread-count to 2 in the suite tag

Step 3: Include LoginTest and SearchTest classes as separate test tags in the suite

Step 4: Run the TestNG suite XML file

Step 5: Observe that LoginTest and SearchTest run at the same time in separate threads

✅ Expected Result: Both LoginTest and SearchTest execute simultaneously without waiting for each other, completing successfully.

Automation Requirements - TestNG with Selenium WebDriver

Assertions Needed:

Verify both test classes complete successfully

Verify tests run in parallel threads (thread IDs differ)

Best Practices:

Use TestNG XML suite file to configure parallel execution

Avoid sharing WebDriver instances between tests

Use thread-safe WebDriver initialization

Use explicit waits instead of Thread.sleep

Automated Solution

Selenium Java

import org.openqa.selenium.WebDriver;
import org.openqa.selenium.chrome.ChromeDriver;
import org.testng.Assert;
import org.testng.annotations.AfterMethod;
import org.testng.annotations.BeforeMethod;
import org.testng.annotations.Test;

public class LoginTest {
    private WebDriver driver;

    @BeforeMethod
    public void setUp() {
        driver = new ChromeDriver();
    }

    @Test
    public void testLogin() {
        driver.get("https://example.com/login");
        String threadName = Thread.currentThread().getName();
        System.out.println("LoginTest running on thread: " + threadName);
        Assert.assertEquals(driver.getTitle(), "Login Page");
    }

    @AfterMethod
    public void tearDown() {
        if (driver != null) {
            driver.quit();
        }
    }
}

// Another test class
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.chrome.ChromeDriver;
import org.testng.Assert;
import org.testng.annotations.AfterMethod;
import org.testng.annotations.BeforeMethod;
import org.testng.annotations.Test;

public class SearchTest {
    private WebDriver driver;

    @BeforeMethod
    public void setUp() {
        driver = new ChromeDriver();
    }

    @Test
    public void testSearch() {
        driver.get("https://example.com/search");
        String threadName = Thread.currentThread().getName();
        System.out.println("SearchTest running on thread: " + threadName);
        Assert.assertTrue(driver.getTitle().contains("Search"));
    }

    @AfterMethod
    public void tearDown() {
        if (driver != null) {
            driver.quit();
        }
    }
}

/* TestNG XML suite file (testng.xml):
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE suite SYSTEM "https://testng.org/testng-1.0.dtd">
<suite name="ParallelSuite" parallel="tests" thread-count="2">
  <test name="LoginTest">
    <classes>
      <class name="LoginTest"/>
    </classes>
  </test>
  <test name="SearchTest">
    <classes>
      <class name="SearchTest"/>
    </classes>
  </test>
</suite>
*/

The solution includes two separate test classes: LoginTest and SearchTest. Each class creates its own WebDriver instance in the @BeforeMethod and closes it in @AfterMethod to avoid sharing drivers between threads.

The TestNG XML suite file configures parallel execution by setting parallel="tests" and thread-count="2". This means TestNG will run the two test classes at the same time in separate threads.

Inside each test, we print the current thread name to the console to confirm parallel execution. Assertions check the page titles to verify the tests run correctly.

This setup follows best practices by isolating WebDriver instances per test and using TestNG's built-in parallel execution features.

Common Mistakes - 4 Pitfalls

Sharing a single WebDriver instance across multiple tests

Using Thread.sleep instead of explicit waits

{'mistake': 'Not configuring parallel attribute in TestNG XML', 'why_bad': 'Tests will run sequentially, not in parallel as intended.', 'correct_approach': 'Set parallel="tests" and thread-count in the TestNG suite XML.'}

Using hardcoded XPath locators that are brittle

Bonus Challenge

Now add data-driven testing to LoginTest with 3 different username and password combinations

Show Hint

Practice

1. What is the main purpose of configuring parallel execution in Selenium with TestNG?

easy

A. To run multiple tests at the same time and save execution time

B. To run tests one after another in a fixed order

C. To increase the number of test cases manually

D. To disable test execution temporarily

Solution

1. Step 1: Understand parallel execution concept

   Parallel execution means running tests simultaneously instead of sequentially.

2. Step 2: Identify the benefit of parallel execution

   Running tests at the same time saves overall test execution time.

3. Final Answer:

   To run multiple tests at the same time and save execution time -> Option A

4. Quick Check:

   Parallel execution = run tests simultaneously [OK]

Hint: Parallel means running tests together to save time [OK]

Common Mistakes:

• Thinking parallel means running tests one by one
• Confusing parallel execution with increasing test count
• Assuming parallel disables tests

2. Which XML attribute correctly sets the number of threads for parallel execution in TestNG?

easy

A. thread-count

B. parallel-count

C. max-threads

D. execution-threads

Solution

1. Step 1: Recall TestNG XML attributes for parallelism

   TestNG uses thread-count to specify how many threads run tests in parallel.

2. Step 2: Verify other options are incorrect

   Attributes like parallel-count, max-threads, and execution-threads are not valid TestNG attributes.

3. Final Answer:

   thread-count -> Option A

4. Quick Check:

   Thread count = number of parallel threads [OK]

Hint: Use thread-count to set parallel threads in TestNG XML [OK]

Common Mistakes:

• Using wrong attribute names like parallel-count
• Confusing thread-count with parallel attribute
• Misspelling thread-count

3. Given this TestNG XML snippet, how many tests will run in parallel?

<suite name="Suite" parallel="tests" thread-count="3">
  <test name="Test1"></test>
  <test name="Test2"></test>
  <test name="Test3"></test>
  <test name="Test4"></test>
</suite>

medium

A. All 4 tests run in parallel

B. 3 tests run in parallel, 1 waits

C. Only 1 test runs at a time

D. 2 tests run in parallel, 2 wait

Solution

1. Step 1: Understand thread-count and parallel attribute

   parallel="tests" means tests run in parallel. thread-count="3" limits max parallel threads to 3.

2. Step 2: Apply thread-count to number of tests

   There are 4 tests but only 3 threads, so 3 tests run simultaneously and 1 waits.

3. Final Answer:

   3 tests run in parallel, 1 waits -> Option B

4. Quick Check:

   thread-count limits parallel tests to 3 [OK]

Hint: thread-count limits max parallel tests running [OK]

Common Mistakes:

• Assuming all tests run parallel ignoring thread-count
• Confusing parallel="tests" with parallel="methods"
• Ignoring that thread-count caps parallelism

4. You configured parallel="methods" and thread-count="2" in TestNG XML, but tests still run sequentially. What is the likely cause?

medium

A. TestNG does not support parallel execution

B. thread-count must be set to 1 for parallel methods

C. Test methods share state and are not thread-safe

D. parallel attribute should be set to "tests" for methods

Solution

1. Step 1: Understand parallel methods and thread safety

   parallel="methods" runs test methods in parallel only if they are thread-safe and independent.

2. Step 2: Identify cause of sequential execution

   If tests share data or state, TestNG runs them sequentially to avoid conflicts.

3. Final Answer:

   Test methods share state and are not thread-safe -> Option C

4. Quick Check:

   Shared state blocks parallel method execution [OK]

Hint: Ensure test methods are independent for parallel execution [OK]

Common Mistakes:

• Setting thread-count to 1 disables parallelism
• Using wrong parallel attribute value
• Believing TestNG lacks parallel support

5. You want to run test classes in parallel but ensure each class uses its own WebDriver instance to avoid conflicts. Which TestNG XML configuration is best?

hard

A. <suite name="Suite" parallel="instances" thread-count="4">

B. <suite name="Suite" parallel="tests" thread-count="4">

C. <suite name="Suite" parallel="methods" thread-count="4">

D. <suite name="Suite" parallel="classes" thread-count="4">

Solution

1. Step 1: Understand parallel modes in TestNG

   parallel="classes" runs test classes in parallel, isolating each class's WebDriver instance.

2. Step 2: Match requirement to configuration

   Running classes in parallel with thread-count=4 allows 4 classes to run simultaneously, each with its own driver.

3. Final Answer:

   <suite name="Suite" parallel="classes" thread-count="4"> -> Option D

4. Quick Check:

   parallel="classes" isolates WebDriver per class [OK]

Hint: Use parallel="classes" for separate WebDriver per class [OK]

Common Mistakes:

• Using parallel="methods" causing shared driver issues
• Choosing parallel="tests" which runs test tags, not classes
• Using parallel="instances" which is less common and may confuse