testng-parallel

What this skill does

# TestNG Parallel Execution

Master TestNG parallel test execution including thread pool configuration, suite-level parallelism, method-level parallelism, and thread safety patterns. This skill covers techniques for maximizing test throughput while maintaining test reliability.

## Overview

TestNG supports parallel execution at multiple levels: suite, test, class, and method. Proper parallel configuration can significantly reduce test execution time, but requires careful consideration of thread safety and resource management.

## Parallel Execution Modes

### Suite-Level Parallelism

Run multiple `<test>` tags in parallel:

```xml
<!DOCTYPE suite SYSTEM "https://testng.org/testng-1.0.dtd">
<suite name="Parallel Suite" parallel="tests" thread-count="3">

    <test name="Chrome Tests">
        <classes>
            <class name="com.example.tests.BrowserTest"/>
        </classes>
    </test>

    <test name="Firefox Tests">
        <classes>
            <class name="com.example.tests.BrowserTest"/>
        </classes>
    </test>

    <test name="Safari Tests">
        <classes>
            <class name="com.example.tests.BrowserTest"/>
        </classes>
    </test>

</suite>
```

### Class-Level Parallelism

Run test classes in parallel:

```xml
<!DOCTYPE suite SYSTEM "https://testng.org/testng-1.0.dtd">
<suite name="Parallel Classes" parallel="classes" thread-count="4">

    <test name="All Tests">
        <classes>
            <class name="com.example.tests.UserServiceTest"/>
            <class name="com.example.tests.ProductServiceTest"/>
            <class name="com.example.tests.OrderServiceTest"/>
            <class name="com.example.tests.PaymentServiceTest"/>
        </classes>
    </test>

</suite>
```

### Method-Level Parallelism

Run test methods in parallel:

```xml
<!DOCTYPE suite SYSTEM "https://testng.org/testng-1.0.dtd">
<suite name="Parallel Methods" parallel="methods" thread-count="5">

    <test name="Service Tests">
        <classes>
            <class name="com.example.tests.IndependentMethodsTest"/>
        </classes>
    </test>

</suite>
```

### Instance-Level Parallelism

Run test instances in parallel (useful with Factory):

```xml
<!DOCTYPE suite SYSTEM "https://testng.org/testng-1.0.dtd">
<suite name="Parallel Instances" parallel="instances" thread-count="3">

    <test name="Factory Tests">
        <classes>
            <class name="com.example.tests.FactoryGeneratedTest"/>
        </classes>
    </test>

</suite>
```

## Thread Pool Configuration

### Basic Thread Configuration

```xml
<!DOCTYPE suite SYSTEM "https://testng.org/testng-1.0.dtd">
<suite name="Thread Pool Suite" parallel="methods" thread-count="10">
    <!-- Global thread pool configuration -->

    <test name="Test Group 1" thread-count="5">
        <!-- Override for this specific test -->
        <classes>
            <class name="com.example.tests.Test1"/>
        </classes>
    </test>

    <test name="Test Group 2">
        <!-- Uses suite-level thread-count -->
        <classes>
            <class name="com.example.tests.Test2"/>
        </classes>
    </test>

</suite>
```

### Data Provider Parallel Execution

```xml
<!DOCTYPE suite SYSTEM "https://testng.org/testng-1.0.dtd">
<suite name="DataProvider Suite" data-provider-thread-count="20">

    <test name="Data Driven Tests">
        <classes>
            <class name="com.example.tests.ParallelDataProviderTest"/>
        </classes>
    </test>

</suite>
```

```java
public class ParallelDataProviderTest {

    @DataProvider(name = "largeDataSet", parallel = true)
    public Object[][] provideLargeDataSet() {
        Object[][] data = new Object[100][2];
        for (int i = 0; i < 100; i++) {
            data[i] = new Object[]{"User" + i, "user" + i + "@example.com"};
        }
        return data;
    }

    @Test(dataProvider = "largeDataSet")
    public void testWithParallelData(String name, String email) {
        System.out.println(Thread.currentThread().getName() + " - Testing: " + name);
        // Each data row runs in parallel
    }
}
```

## Thread Safety Patterns

### Thread-Local Storage

```java
import org.testng.annotations.*;

public class ThreadLocalTest {

    // Thread-local storage for test-specific resources
    private static ThreadLocal<WebDriver> driverThread = new ThreadLocal<>();
    private static ThreadLocal<String> sessionThread = new ThreadLocal<>();

    @BeforeMethod
    public void setUp() {
        // Initialize thread-local resources
        driverThread.set(createWebDriver());
        sessionThread.set(generateSessionId());
    }

    @AfterMethod
    public void tearDown() {
        // Clean up thread-local resources
        WebDriver driver = driverThread.get();
        if (driver != null) {
            driver.quit();
        }
        driverThread.remove();
        sessionThread.remove();
    }

    @Test
    public void testParallelBrowser() {
        WebDriver driver = driverThread.get();
        String session = sessionThread.get();
        System.out.println("Thread: " + Thread.currentThread().getName() +
                          " Session: " + session);
        // Use thread-local driver
    }

    private WebDriver createWebDriver() {
        // Create browser instance
        return new ChromeDriver();
    }

    private String generateSessionId() {
        return UUID.randomUUID().toString();
    }
}
```

### Synchronized Shared Resources

```java
import org.testng.annotations.*;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.ConcurrentHashMap;

public class SynchronizedResourceTest {

    // Thread-safe counter
    private static AtomicInteger testCounter = new AtomicInteger(0);

    // Thread-safe collection
    private static ConcurrentHashMap<String, String> sharedCache = new ConcurrentHashMap<>();

    // Lock object for critical sections
    private static final Object lock = new Object();

    @Test(threadPoolSize = 5, invocationCount = 100)
    public void testAtomicOperations() {
        int count = testCounter.incrementAndGet();
        System.out.println("Test count: " + count);
    }

    @Test(threadPoolSize = 3, invocationCount = 50)
    public void testConcurrentMap() {
        String threadName = Thread.currentThread().getName();
        sharedCache.put(threadName, String.valueOf(System.currentTimeMillis()));
        // Thread-safe without explicit synchronization
    }

    @Test(threadPoolSize = 2, invocationCount = 10)
    public void testSynchronizedBlock() {
        synchronized (lock) {
            // Critical section - only one thread at a time
            performCriticalOperation();
        }
    }

    private void performCriticalOperation() {
        // Operations that require exclusive access
    }
}
```

### Immutable Test Data

```java
import java.util.Collections;
import java.util.List;
import java.util.Arrays;

public class ImmutableDataTest {

    // Immutable test data - inherently thread-safe
    private static final List<String> TEST_USERS = Collections.unmodifiableList(
        Arrays.asList("user1", "user2", "user3", "user4", "user5")
    );

    private static final Map<String, String> CONFIG = Collections.unmodifiableMap(
        Map.of(
            "url", "https://api.example.com",
            "timeout", "30000",
            "retries", "3"
        )
    );

    @Test(threadPoolSize = 5, invocationCount = 20)
    public void testWithImmutableData() {
        // Safe to read from multiple threads
        int userIndex = ThreadLocalRandom.current().nextInt(TEST_USERS.size());
        String user = TEST_USERS.get(userIndex);
        String url = CONFIG.get("url");

        System.out.println(Thread.currentThread().getName() +
                          " - User: " + user + ", URL: " + url);
    }
}
```

## Test Isolation Patterns

### Independent Test Methods

```java
public class IndependentTestsExample {

    // Each test method is completely independent
    @Test
    public void te