Erro ao executar teste

Class not found br.com.caelum.teste.UsuariosSystemTest java.lang.ClassNotFoundException: br.com.caelum.teste.UsuariosSystemTest at java.net.URLClassLoader.findClass(URLClassLoader.java:381) at java.lang.ClassLoader.loadClass(ClassLoader.java:424) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331) at java.lang.ClassLoader.loadClass(ClassLoader.java:357) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.loadClass(RemoteTestRunner.java:685)

package br.com.caelum.teste;


import static org.junit.Assert.assertTrue;
import org.junit.Test;
import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.firefox.FirefoxDriver;

public class UsuariosSystemTest {

     @Test
    public void deveAdicionarUmUsuario() {
        WebDriver driver = new FirefoxDriver();
        // 1) pega(get) o link da pagina
        driver.get("http://localhost:8080/usuarios/new");