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Understanding difference between @Factory and @DataProvider in TestNG

@DataProvider: for a single running instance of script, all methods (which consumes dataprovider) are executed for data provided by DataProvider

@Factory: all methods are executed a TestNG class, in different instances.

eg. DataProvider example:
————————-

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

public class DataProviderClass {

@BeforeClass
public void beforeClass() {
System.out.println(“@BeforeClass is called”);
}

@Test(dataProvider = “myDP”, dataProviderClass = SimpleTestFactory.class)
public void testMethod(String param) {
System.out.println(“Param from data provider is : ” + param);
}

}

import org.testng.annotations.DataProvider;

public class SimpleTestFactory {
@DataProvider
public Object[][] myDP() {
return new Object[][] { { “Jack” }, { “Joe” } };
}
}

On running DataProviderClass, OUTPUT:
————————————-

@BeforeClass is called
Param from data provider is : Jack
Param from data provider is : Joe
….
===============================================
Default test
Tests run: 2, Failures: 0, Skips: 0
===============================================

@Factory example:
—————–

import org.openqa.selenium.os.Kernel32;
import org.testng.annotations.BeforeClass;
import org.testng.annotations.Factory;
import org.testng.annotations.Test;

public class SimpleTest {
private String param = “”;

public SimpleTest(String param) {
this.param = param;
}

@BeforeClass
public void beforeClass() {
System.out.println(“Before SimpleTest class executed.”+Kernel32.INSTANCE.GetCurrentProcessId());
}

@Test
public void testMethod() {
System.out.println(“testMethod parameter value is: ” + param);
}

@Factory
public Object[] factoryMethod() {
return new Object[] { new SimpleTest(“one”), new SimpleTest(“two”) };
}
}

OUTPUT:
———

Before SimpleTest class executed.18216
testMethod parameter value is: two
Before SimpleTest class executed.18216
testMethod parameter value is: one
…

===============================================
Default test
Tests run: 2, Failures: 0, Skips: 0
===============================================

As you can see, with @Factory implementation, beforeClass method is executed before each execution of testMethod. This shows that factory implementation executes the test method for each individual instance of the test class.