Seeing NullPointerException on running TestNG Selenium Framework

Question

Written the Test Script in TestNG framework where the Open browser activity is happening in "baseClass" under @BeforeTest annotation and the Test Script is written in Test Packages under as @Test Annotation. IN the test Script I am extending the Base Class so that my @beforetest(opening the browser) will work first and then test case functionality should execute. But at TestScript I am getting NULLPointerException. @BeforeTest methods are returning the webdriver object and I thought it will work at @Test methods but this is failing

Can anyone guide me here how to proceed further?

public class BaseClass {
    public WebDriver driver;
    @BeforeTest
    public WebDriver openBrowser()
    {
        System.setProperty("webdriver.gecko.driver", System.getProperty("user.dir")+"/Drivers/geckodriver.exe");
        driver = new FirefoxDriver();
        driver.manage().timeouts().implicitlyWait(Duration.ofSeconds(120));
        driver.manage().window().maximize();
        driver.get("https://app.vwo.com/#/analyze/heatmap/129/reports?token=eyJhY2NvdW50X2lkIjo2LCJleHBlc%20mltZW50X2lkIjoxMjksImNyZWF0ZWRfb24iOjE1MDc3ODk0ODcsInR5cGUiOiJjYW1wYWlnbiIsI%20nZlcnNpb24iOjEsImhhc2giOiJiMzlmMTQ4MWE0ZDMyN2Q4MDllNTM1YzVlNWFjOGVlMCJ9");
        return driver;
    }

public class Assignment extends BaseClass {
    WebDriver driver;
    CommonMethods common = new CommonMethods();
    
    @Test
    public void executeTest()
    {
        WebElement heatMap_locator=driver.findElement(By.xpath(common.readPropertyFile("viewheatmap_xpath")));
        common.clickJavaScriptExecutor(driver, heatMap_locator);
}

Answer 1

If you extend a class having driver field where that field is initialized do not add filed of the same name to child class. Doing that you're hiding a field of base class.

Here is the example:

Your base:

public class TestBase {

    public Object object;

    @BeforeTest
    public void doBefore(){
        object = new Object();
    }

}

Your test that WILL fail (a.k.a BAD TEST):

public class TestChild extends TestBase{

    Object object;

    @Test
    public void doTest(){
        Assert.assertNotNull(object);
    }

}

Your test that WON'T fail (a.k.a GOOD TEST):

public class TestChild extends TestBase{

    @Test
    public void doTest(){
        Assert.assertNotNull(object);
    }

}

Answer 2

Create a base class where you write a method of initializing. then you an extend that class to your main test case, then you can initialize that method of initializing in @beforeTest

public static void initConfiguration(){
    System.setProperty("webdriver.chrome.driver",
                    System.getProperty("user.dir") + "\\src\\test\\resources\\executables\\chromedriver.exe");
 driver = new ChromeDriver(options);
 driver.get(baseurl);
 driver.manage().window().maximize();
}

above code, you can write in base class then extend that class to your testcase class.