How can I mock dependencies which aren't interfaces but subclasses?

Question

I'm not sure if my design is simply stupid, or there's a good way to make it work. Consider the following classes:

public abstract class CheckBase {
    protected Collector collector;

    public void addData(String data) {
        collector.addData(data);
    }

    public void setCollector(Collector collector) {
        this.collector = collector;
    }
}

interface Collector {
    void addData(String data);
}


final class DogCheck extends CheckBase {
    public void someCheck() {
        // check
        addData("SomeData");
    }
}

class ClassWithDependencies {
    private final DogCheck dogCheck;

    public ClassWithDependencies(DogCheck dogCheck) {
        this.dogCheck = dogCheck;
    }
}

Now I want to test something in ClassWithDependencies, which does not need DogCheck, or should have a mock version of it.

How can I do this?