TestNG抛出“ java.lang.NullPointerException”

Question

I am trying to execute my webdriver code using testng.xml (using @Test(groups = {"General"}))

The code works perfectly fine without using testng.xml. I right click "ChapterOne.java" and perform Run As > TestNG Test

But when I configure testng.xml, it gives throws exception. Console shows only the below information:

> [TestNG] Running:
>  G:\Webdriver_JUnit\BookAutomatedTester_TestNG\testng.xml
> ===============================================
> Suite1
> Total tests run: 3, Failures: 3, Skips: 0
> ===============================================

The generated "index.html" report shows the below message for all methods that are annotated with @Test(groups = {"General"}):

>  VerifyChapter1DropDown java.lang.NullPointerException
> at test.ChapterOne.VerifyChapter1DropDown(ChapterOne.java:44)
> ... Removed 24 stack frames

This is confusing as NullPointerException is thrown by java and not TestNG.

Below is my selenium code:

package test;
import java.util.Set;

import org.testng.annotations.*;
import org.openqa.selenium.*;
import org.openqa.selenium.firefox.FirefoxDriver;
import org.openqa.selenium.remote.RemoteWebDriver;
import org.testng.*;

public class ChapterOne  {

    WebDriver _driver;
    String ActualText;
    String baseurl = "http://book.theautomatedtester.co.uk/chapter1";
    WebElement AjaxTextLoc;

    @BeforeClass
    public void SetUp() {
        _driver = new FirefoxDriver();
        _driver.get(baseurl);   }

    @Test (groups = { "General" })
    public void VerifyChapter1Text()    {
        WebElement WDText = _driver.findElement(By.xpath("/html/body/div[2]/p[1]"));
        String ActualText = "If you have arrived here then you have installed Selenium IDE and are ready to start recording your first test.";
        Assert.assertEquals(ActualText, WDText.getText() );

        WebElement WDText1 = _driver.findElement(By.id("divontheleft"));
        ActualText = "Assert that this text is on the page";
        Assert.assertEquals(ActualText, WDText1.getText());
        ((JavascriptExecutor) _driver).executeScript("window.scrollBy(0,200)", "");
        ((JavascriptExecutor) _driver).executeScript("alert('hello world');");
                }           
    @Test (groups = { "General" })
    public void VerifyChapter1RadioButton() {
        WebElement RadioBtn = _driver.findElement(By.id("radiobutton"));
        Assert.assertEquals(RadioBtn.isSelected(), false);
        RadioBtn.click();
        Assert.assertEquals(RadioBtn.isSelected(), true);
        }
    @Test (groups = { "General" })
    public void VerifyChapter1DropDown()    {
        WebElement DropDn = _driver.findElement(By.id("selecttype"));
        DropDn.click();     // extra step
        DropDn.sendKeys("Selenium Grid");       
        }   
    @Test(groups = {"Different"})
    public void VerifyChapter1CheckBox()    {
        WebElement CheckBx = _driver.findElement(By.name("selected(1234)"));
        Assert.assertEquals(CheckBx.isEnabled(), true);
        Assert.assertEquals(CheckBx.isSelected(), false);
        CheckBx.click();
        Assert.assertEquals(CheckBx.isSelected(), true);        
        }
    @Test(groups = {"Different"})
    public void VerifyChapter1Btns()    {
        WebElement Btn1Text = _driver.findElement(By.id("html5div"));
        Btn1Text.clear();
        WebElement Btn1 = _driver.findElement(By.id("secondajaxbutton"));
        Assert.assertEquals(Btn1.isEnabled(), true);    
        Btn1.click();
        ActualText = "I have been added with a timeout";
        Assert.assertEquals(ActualText, Btn1Text.getText());            
        }
    @Test(groups = {"Different"})
    public void VerifyChapter1SwitchWindows()   {
        String ParentHandle = _driver.getWindowHandle();
        _driver.findElement(By.id("multiplewindow")).click();
        Set<String> AllHandles = _driver.getWindowHandles();

        for(String ChildHandle : AllHandles)    {
            _driver.switchTo().window(ChildHandle);     
        }
        _driver.close();
        _driver.switchTo().window(ParentHandle);        

        }
    @Test(groups = {"Different"})
    public void VerifyChapter1AJAX() throws Exception   {
        WebElement AjaxBtnTxt = _driver.findElement(By.id("loadajax"));
        AjaxBtnTxt.click();
        ActualText = "The following text has been loaded from another page on this site. It has been loaded in an asynchronous fashion so that we can work through the AJAX section of this chapter";
        Thread.sleep(1000);     
        WebElement AjaxTextLoc = _driver.findElement(By.xpath("//div[@id='ajaxdiv']/p"));
        Assert.assertEquals(ActualText, AjaxTextLoc.getText());
        ((RemoteWebDriver) _driver).executeScript("window.scrollBy(0,-200)", "");

        }

    @AfterClass
    public void Quit()  {
        System.out.println("@AfterClass was executed");
        _driver.quit();
    }       
    }

Below is the testng.xml:

<suite name="Suite1">
  <test name="My ChapterOne Tests">
    <groups>  
        <run>
        <include name="General" />
        </run>
    </groups>
        <classes>
        <class name="test.ChapterOne" />
        </classes>
    </test>
</suite>

PS: I am new to webdriver programming and I'm still learning. I tried hard to find out what could be the issue but couldn't figure out.

Update:

I tweaked my code by removing all Selenium Code from the functions. I added print statements. Please see below:

    @Test(groups={"General"})
    public void VerifyChapter1Text()    {
        System.out.println("In VerifyChapter1Text");
                }           

    @Test (groups = { "General" })
    public void VerifyChapter1RadioButton() {
        System.out.println("In VerifyChapter1RadioButton");
        }
    @Test (groups = { "General" })
    public void VerifyChapter1DropDown()    {
        System.out.println("In VerifyChapter1DropDown");
        }   

To my surprise it worked. That means that my testng.xml file is correct.

But how is this possible? My original webdriver code works perfectly without using testng.xml.

Answer 1

The following perhaps can't find anything and returns null :

WebElement DropDn = _driver.findElement(By.id("selecttype"));

Test if _driver.findElement(By.id("selecttype")) actually returns an element.

Answer 2

您应该添加@BeforeClass(alwasyRun = true) ，然后重试。