How to unit test abstract classes: extend with stubs?

Question

I was wondering how to unit test abstract classes, and classes that extend abstract classes.

Should I test the abstract class by extending it, stubbing out the abstr

Answer 1

Following @patrick-desjardins answer, I implemented abstract and it's implementation class along with @Test as follows:

Abstract class - ABC.java

import java.util.ArrayList;
import java.util.List;

public abstract class ABC {

    abstract String sayHello();

    public List getList() {
        final List defaultList = new ArrayList<>();
        defaultList.add("abstract class");
        return defaultList;
    }
}

As Abstract classes cannot be instantiated, but they can be subclassed, concrete class DEF.java, is as follows:

public class DEF extends ABC {

    @Override
    public String sayHello() {
        return "Hello!";
    }
}

@Test class to test both abstract as well as non-abstract method:

import org.junit.Before;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.empty;
import static org.hamcrest.Matchers.is;
import static org.hamcrest.Matchers.not;
import static org.hamcrest.Matchers.contains;
import java.util.Collection;
import java.util.List;
import static org.hamcrest.Matchers.equalTo;

import org.junit.Test;

public class DEFTest {

    private DEF def;

    @Before
    public void setup() {
        def = new DEF();
    }

    @Test
    public void add(){
        String result = def.sayHello();
        assertThat(result, is(equalTo("Hello!")));
    }

    @Test
    public void getList(){
        List result = def.getList();
        assertThat((Collection) result, is(not(empty())));
        assertThat(result, contains("abstract class"));
    }
}