O navegador não está sendo fechado no final

import static org.junit.Assert.assertTrue;

import org.junit.Test;
import org.openqa.selenium.By;
import org.openqa.selenium.Keys;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.firefox.FirefoxDriver;

public class UsuarioSystemTestInvalido {


       @Test
        public void naoDeveAdicionarUmUsuarioSemNome() {
           System.setProperty("webdriver.gecko.driver", "C:\\Program Files\\GeckoDriver\\geckodriver.exe");
            WebDriver driver = new FirefoxDriver();
            driver.get("http://localhost:8080/usuarios/new");

            WebElement email = driver.findElement(By.name("usuario.email"));

            email.sendKeys("ronaldo2009@terra.com.br");
            email.submit();

            assertTrue(driver.getPageSource().contains("Nome obrigatorio!"));

            driver.close();

        }
}