How does TestNG invoke a test method using multiple threads?

TestNG supports multi-threading, i.e., a @Test method can be invoked multiple times in parallel. A test method should be invoked from multiple threads so that multiple invocation is also required. If we want to run a single @Test at multi-thread, it is of no use. Therefore, multi-thread is useful if a @Test method needs to be run multiple times asynchronously.

Multi-threading can be achieved by using the keyword threadPoolSize = at @Test. However, to invoke a method multiple times, another keyword invocationCount =  is required. Combining these two keywords, we can achieve multi-threading. For example,

@Test(threadPoolSize=5, invocationCount = 10)

In this example, the @Test method will execute for a total of 10 times from 5 threads. Note that the count of total execution is 10 from 5 different threads. It doesn't mean that @Test will run a total of 50 times or 10 times in each thread. It simply means, 5 threads will execute the method a total of 10 times.

In this article, we will illustrate how to achieve multithreading in TestNG.

Approach/Algorithm to solve this problem −

• Step 1 − Create a TestNG class called NewTestngClass.

• Step 2 − Write a @Test method in the class, as shown in the program code section. Add threadPoolSize and invocationCount

• Step 3 − Now create the testNG.xml to run the TestNG classes.

• Step 4 − Run the testNG.xml or run the testNG class directly in IDE or compile and run it using command line.

In the output, you can notice that there are 5 threads are running in parallel (Thread ID 12 to 16) and the method runs for a total of 10 times.

Example

Use the following code for the common TestNG class "NewTestngClass" −

src/ NewTestngClass.java

import org.testng.ITestContext;
import org.testng.annotations.*;
public class NewTestngClass {
   @Test(threadPoolSize = 5, invocationCount = 10)
   public void testcase1(ITestContext testContext){
      System.out.println("Thread ID: "+Thread.currentThread().getId());
      int currentCount = testContext.getAllTestMethods()[0].getCurrentInvocationCount();
      System.out.println("Executing count: " + currentCount);
   }
}

testng.xml

This is a configuration file that is used to organize and run the TestNG test cases. It is very handy when limited tests are needed to execute rather than the full suite.

<?xml version = "1.0" encoding = "UTF-8"?>
<!DOCTYPE suite SYSTEM "http://testng.org/testng-1.0.dtd" >
<suite name = "Suite1">
   <test name = "test1">
      <classes>
         <class name = "NewTestngClass"/>
      </classes>
   </test>
</suite>

Output

Thread ID: 12
Thread ID: 13
Thread ID: 16
Thread ID: 14
Executing count: 0
Thread ID: 15
Executing count: 0
Executing count: 0
Executing count: 0
Executing count: 0
Thread ID: 15
Executing count: 5
Thread ID: 12
Executing count: 6
Thread ID: 13
Executing count: 7
Thread ID: 14
Executing count: 8
Thread ID: 15
Executing count: 9

===============================================
Suite1
Total tests run: 10, Passes: 10, Failures: 0, Skips: 0
===============================================================