What is @Factory Annotation?

TestNG Factory annotation feature allows us to create tests dynamically at run-time. Factory will execute all the @Test methods in the test class using a separate instance of the test class.

We will go through a code example to explain about @Factory annotated method.

Code Listing

package com.testingdocs.testng.sample;

import org.testng.annotations.AfterClass;
import org.testng.annotations.BeforeClass;
import org.testng.annotations.Test;

public class FactoryExampleClass 
{
 String testdata ;
 int objectID ;
 
 public FactoryExampleClass(int ojectID, String testdata)
 {
 this.objectID = ojectID ;
 this.testdata= testdata ;
 }
 
 @BeforeClass 
 public void beforeClass(){ 
 System.out.println("This is before class of " + objectID); 
 } 
 
 @Test 
 public void testmethod(){ 
 System.out.println("This is test method, testdata is :" + testdata); 
 }
 
 @AfterClass 
 public void afterClass(){ 
 System.out.println("This is after class of " + objectID); 
 } 

}

Now we would write the @Factory method which runs 3 times as shown below.

package com.testingdocs.testng.sample;

import org.testng.annotations.Factory;

public class TestNGFactory 
{
 
 @Factory
 public static Object[] testData()
 { 
 Object[] object = new Object[3]; 
 
 object[0]= new FactoryExampleClass(1,"testdata1"); 
 object[1]= new FactoryExampleClass(2,"testdata2"); 
 object[2]= new FactoryExampleClass(3,"testdata3"); 
 
 return object; 
 } 
}

Run result

This is before class of 1
This is test method, testdata is  :testdata1
This is after class of 1
This is before class of 3
This is test method, testdata is  :testdata3
This is after class of 3
This is before class of 2
This is test method, testdata is  :testdata2
This is after class of 2

PASSED: testmethod
PASSED: testmethod
PASSED: testmethod

===============================================
Default test
Tests run: 3, Failures: 0, Skips: 0
===============================================

Look how we have executed the test method multiple times run-time for different testdata . ( 3 times in the above example )

Common Problem

Common problems are exceptions in Factory methods. Any exception in the factory method would throw an exception like as shown below sample exception trace.:

org.testng.TestNGException:
The factory method class com.testingdocs.testng.sample.TestNGFactory.testData() threw an exception

We need to debug the root cause of the exception in the factory method.TestNG internal code that displays the error is as shown below:

catch (Throwable t) {
 ConstructorOrMethod com = getConstructorOrMethod();
 throw new TestNGException("The factory method "
 + com.getDeclaringClass() + "." + com.getName()
 + "() threw an exception", t);
 }