How to get ConnectionFactory from JNDI for testing

Im using Spring-Test (Not Spring project) for setting the JNDI at my unit test cases. But i cant get the ConnectionFactory implementation;

    @Before
    public static void setUp() throws NamingException {

    SimpleNamingContextBuilder builder =  SimpleNamingContextBuilder.emptyActivatedContextBuilder();

    // I cant instance ConnectionFactory (its an interface)
    ConnectionFactoryImplStub cf = new ConnectionFactoryImplStub();

    builder.bind("ECI", cf);
    }

So when i test my methods, the test dont gives error, but when the connection is builded, it doesnt do nothing, because "ConnectionFactoryImplStub" is a class made by me, that implements ConnectionFactory (and it overrides all ConnectionFactory methods).

Is there any other way i can make the setUp without ConnecionFactoryImplStub? Or any other way to solve this problem. PD: Legacy code, cant touch it.