How to simulate a user logged into an application with Demoiselle 2.4.2?

I have a Demoiselle 2.4.2 application already running that needs to use SecurityContext to get the User currently logged in and make some decisions. The time now is to write the unit tests using JUnit 4 for this application (they were not made in the application genesis, but we want to do it now). At this point the problem arises that there is no logon process that precedes the execution of test cases.

By what technique can you simulate the logon process, so that when instances of SecurityContext are injected over the controllers of the application in test cases), will these respond to the user I need?

Update 1

To make the situation easier to understand, it follows the code of the class that implements the unit test:

@RunWith(DemoiselleRunner.class)
public class CaixaOperacaoTests {

    @Inject
    static private Credentials credentials;

    @Inject
    private CaixaOperacaoBC caixaOperacao;

    @Before
    public void setUp() throws Exception {
        credentials.setUsername("meususario");
        credentials.setPassword("minhasenha");
    }

    @Test
    public void shouldAbrirCaixaComUsuarioLogado() {
        // Arrange
        BigDecimal valorAbertura = new BigDecimal(10.50);

        // Act
        CaixaSessao sessao = caixaOperacao.abrirCaixa(valorAbertura, null);

        // Assert
        assertThat(sessao, notNullValue());
    }
}

Follow the SecurityServices code:

@ApplicationScoped
public class SecurityServices {
    @Inject
    SecurityContext securityContext;
    @Inject
    PessoaBC pessoaBC;

    public Long idPessoaFisicaDoUsuarioLogado(){
        Long idPessoa = (Long) securityContext.getUser().getAttribute(UsuarioSession.Fields.PESSOA_ID);
        return idPessoa;
    }

    public Pessoa pessoaFisicaDoUsuarioLogado(){
        Long idPessoa = idPessoaFisicaDoUsuarioLogado();
        return pessoaBC.load(idPessoa);
    }

    SecurityContext getContext() {
        return securityContext;
    }
}

Note that in the idPessoaFisicaDoUsuarioLogado() method there is the use of securityContext , which has value. However, the getUser() method returns null from where all my problems come from.

Of course, the credential definition can not occur in the unit test class, it has to occur before, but where?