Parallel execution configuration in Selenium Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of TestNG Parallel Execution Configuration

Given the following TestNG XML configuration for parallel execution, what will be the output order of test methods if each test prints its method name when run?

Selenium Java

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE suite SYSTEM "https://testng.org/testng-1.0.dtd">
<suite name="Suite" parallel="methods" thread-count="2">
  <test name="Test1">
    <classes>
      <class name="tests.SampleTest"/>
    </classes>
  </test>
</suite>

// SampleTest.java
package tests;
import org.testng.annotations.Test;
public class SampleTest {
  @Test
  public void testA() {
    System.out.println("testA");
  }
  @Test
  public void testB() {
    System.out.println("testB");
  }
  @Test
  public void testC() {
    System.out.println("testC");
  }
}

A testA\ntestB\ntestC (order may vary but all run concurrently with max 2 threads)

B testA\ntestB\ntestC (always sequential in this order)

C testA\ntestC\ntestB (always this fixed order)

D Only testA runs because thread-count limits to 1

💡 Hint

Parallel execution with thread-count=2 means up to 2 tests run at the same time, order is not guaranteed.

With parallel="methods" and thread-count=2, TestNG runs up to 2 test methods simultaneously. The order of printed output can vary because tests run concurrently, but all tests will run.

❓ assertion

intermediate

Correct Assertion for Parallel Test Execution Completion

In a Selenium TestNG parallel test suite, which assertion correctly verifies that all tests have completed execution before proceeding?

Selenium Java

import org.testng.Assert;
import org.testng.annotations.Test;

@Test
public void verifyAllTestsCompleted() {
  boolean allTestsDone = TestExecutionListener.allTestsFinished();
  // Which assertion below is correct to confirm all tests finished?
}

A Assert.assertFalse(allTestsDone, "Not all tests completed");

B Assert.assertNull(allTestsDone, "Not all tests completed");

C Assert.assertTrue(allTestsDone, "Not all tests completed");

D Assert.assertEquals(allTestsDone, false, "Not all tests completed");

💡 Hint

You want to confirm the boolean flag is true indicating completion.

The variable allTestsDone is true when all tests finish. Assert.assertTrue checks this condition correctly.

🔧 Debug

advanced

Debugging Thread Safety Issue in Parallel Selenium Tests

You have configured parallel execution in TestNG with thread-count=3. Your Selenium tests share a WebDriver instance stored in a static variable. What problem will most likely occur?

A Tests will throw a compilation error due to static WebDriver.

B Tests will run faster without any issues because WebDriver is shared.

C Tests will run sequentially ignoring parallel configuration.

D Tests will fail intermittently due to WebDriver instance conflicts across threads.

💡 Hint

Consider thread safety when sharing objects in parallel tests.

Sharing a single WebDriver instance across multiple threads causes conflicts and unpredictable failures because WebDriver is not thread-safe.

❓ framework

advanced

Best Practice for Parallel Execution in Selenium with TestNG

Which TestNG suite XML configuration snippet correctly enables parallel execution at the class level with 4 threads?

A

<suite name="Suite" parallel="classes" thread-count="4">
  <test name="Test">
    <classes>
      <class name="tests.TestClass1"/>
      <class name="tests.TestClass2"/>
    </classes>
  </test>
</suite>

B

<suite name="Suite" parallel="tests" thread-count="4">
  <test name="Test1">
    <classes>
      <class name="tests.TestClass1"/>
    </classes>
  </test>
  <test name="Test2">
    <classes>
      <class name="tests.TestClass2"/>
    </classes>
  </test>
</suite>

C

<suite name="Suite" parallel="methods" thread-count="4">
  <test name="Test">
    <classes>
      <class name="tests.TestClass1"/>
      <class name="tests.TestClass2"/>
    </classes>
  </test>
</suite>

D

<suite name="Suite" parallel="instances" thread-count="4">
  <test name="Test">
    <classes>
      <class name="tests.TestClass1"/>
      <class name="tests.TestClass2"/>
    </classes>
  </test>
</suite>

💡 Hint

Parallel at class level means parallel="classes" in suite tag.

Setting parallel="classes" with thread-count=4 runs test classes in parallel with up to 4 threads.

🧠 Conceptual

expert

Impact of Parallel Execution on Test Data Management

In a Selenium TestNG suite running tests in parallel, what is the best approach to manage test data to avoid flaky tests?

A Share a single global data object across all tests to reduce memory usage.

B Use thread-local storage or separate data instances per test thread to isolate test data.

C Load test data once before suite and reuse it without synchronization.

D Use static variables to store test data accessible by all threads.

💡 Hint

Think about data isolation in parallel environments.

Sharing data without isolation causes race conditions and flaky tests. Using thread-local or separate data per thread ensures test independence.

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