How to do unit testing without the use of a library?

Question

I've never written a single unit test. But since every article I read, they are talking about unit testing. I figured I should get started with it.

But how?

Can someone point me to a very simple unit tested hello world example? Without the use of jUnit or the likes.

Answer 1

If you don't want to use any other libraries then you have to do a lot of work yourself. For example, suppose you have a class with one function that you want to test:

class Foo {
    public int bar(int input);
}

You can now write a test class:

class TestFoo {
    public void testBarPositive() {
        Foo foo = new Foo();
        System.out.println(foo.bar(5) == 7);
    }

    public void testBarNegative() {
        Foo foo = new Foo();
        System.out.println(foo.bar(-5) == -7);
    }

    public static void main(String[] args) {
        TestFoo t = new TestFoo();
        t.testBarPositive();
        t.testBarNegative();
    }
}

This is a very basic example but it shows you how you could write your own unit tests.

That said, I strongly recommend using a library like JUnit. It gives you a lot for free and removes a huge amount of boiler-plate code that you would have to write yourself. It also generates nice reports and (when combined with something like Cobertura) can give you a fairly comprehensive view of how complete your testing is.