public class BaseSetup {
    private WebDriver driver;

    public WebDriver getDriver() {
        return driver;
    }

    private void setDriver(String browserType, String appURL) {
        switch (browserType) {
        case "chrome":
            driver = initChromeDriver(appURL);
            break;
        case "firefox":
            driver = initFirefoxDriver(appURL);
            break;
    }

    private static WebDriver initChromeDriver(String appURL) {
        ...
    }

    private static WebDriver initFirefoxDriver(String appURL) {

        WebDriver driver = new FirefoxDriver();
        driver.navigate().to(appURL);
        return driver;
    }

    @Parameters({ "browserType", "appURL" })
    @BeforeSuite
    public void initializeTestBaseSetup(String browserType, String appURL) {
        try {
            setDriver(browserType, appURL);

        } catch (Exception e) {
            System.out.println("Error....." + e.getStackTrace());
        }
    }

    @AfterTest
    public void tearDown() {}

public class LoginPage {

//web elements of login page
protected WebDriver driver;
private By txtUsername = By.xpath(".//*[@id='email']");
private By txtPassword = By.xpath(".//*[@id='pass']");
private By btnlogin = By.xpath(".//*[@id='loginbutton']");
private String lblError = null;

//constructor
public LoginPage(WebDriver driver) {
    this.driver = driver;
}

//verify using incorrect password

//enter username into username textbox
public void enterUsername (String username){
    WebElement txtname = driver.findElement(txtUsername);
    if (txtname.isDisplayed())
    {
        txtname.sendKeys(username);
    }
}

//enter password into password textbox
public void enterPassword (String password){
    WebElement txtpw = driver.findElement(txtPassword);
    if (txtpw.isDisplayed())
    {
        txtpw.sendKeys(password);
    }
}

public void clickOnLoginBtn (){
}

public class LoginPageTest extends BaseSetup {

private WebDriver driver;
private LoginPage loginPage;

@Test
public void verifyLoginFunction() {

  loginPage = new LoginPage(driver);
  loginPage.enterUsername("abcdef");
  loginPage.enterPassword("abcdef");
  loginPage.clickOnLoginBtn();

}
@BeforeClass
public void Setup() {
  driver=getDriver();
}
}

private WebDriver driver;
  private LoginPage loginPage;

  @Test
  public void verifyLoginMessage() {
      loginPage = new LoginPage(driver);
      loginPage.enterUsername("abc");
      loginPage.clickOnLoginBtn();
      String errorMsg = loginPage.getErrorMessage();
      System.out.println(errorMsg);
  }


  @BeforeClass
  public void Setup() {
      driver=getDriver();
  }
}

java.lang.NullPointerException
    at com.facebook.objects.LoginPage.enterUsername(LoginPage.java:56)
    at com.facebook.tests.LoginPageTest.verifyLoginFunction(LoginPageTest.java:28)
... Removed 25 stack frames