How to test abstract class in Java with JUnit?

Question

I am new to Java testing with JUnit. I have to work with Java and I would like to use unit tests.

My problem is: I have an abstract class with some abstract methods. But there are some methods which are not abstract. How can I test this class with JUnit? Example code (very simple):

abstract class Car {

    public Car(int speed, int fuel) {
        this.speed = speed;
        this.fuel = fuel;
    }

    private int speed;
    private int fuel;

    abstract void drive();

    public int getSpeed() {
        return this.speed;
    }

    public int getFuel() {
        return this.fuel;
    }
}

I want to test getSpeed() and getFuel() functions.

Similar question to this problem is here, but it is not using JUnit.

In JUnit FAQ section, I found this link, but I don't understand what the author want to say with this example. What does this line of code mean?

public abstract Source getSource() ;

Answer 1

If you have no concrete implementations of the class and the methods aren't static whats the point of testing them? If you have a concrete class then you'll be testing those methods as part of the concrete class's public API.

I know what you are thinking "I don't want to test these methods over and over thats the reason I created the abstract class", but my counter argument to that is that the point of unit tests is to allow developers to make changes, run the tests, and analyze the results. Part of those changes could include overriding your abstract class's methods, both protected and public, which could result in fundamental behavioral changes. Depending on the nature of those changes it could affect how your application runs in unexpected, possibly negative ways. If you have a good unit testing suite problems arising from these types changes should be apparent at development time.