testng中怎么取不到属性值。。。

package ENSG;

import org.openqa.selenium.WebDriver;
import org.openqa.selenium.firefox.FirefoxDriver;
//import org.openqa.selenium.htmlunit.HtmlUnitDriver;
import org.testng.annotations.*;
import static org.testng.Assert.*;
import com.thoughtworks.selenium.*;
import org.openqa.selenium.By;
import org.openqa.selenium.WebElement;

@Test
public class headerBar {

public void msnlogo() {
 WebDriver driver = new FirefoxDriver();
 //WebDriver driver = new HtmlUnitDriver();  
        driver.get("http://xin.msn.com/default.aspx");
        WebElement headlogo=driver.findElement(By.id("headlogo"));
        String width = headlogo.getAttribute("src");
        System.out.println(width);
 }   
}