annotation to make a private method public only for test classes [duplicate]

Answer 1

You can't do this, since then how could you even compile your tests? The compiler won't take the annotation into account.

There are two general approaches to this

The first is to use reflection to access the methods anyway

The second is to use package-private instead of private, then have your tests in the same package (but in a different module). They will essentially be private to other code, but your tests will still be able to access them.

Of course, if you do black-box testing, you shouldn't be accessing the private members anyway.

Answer 2

If your test coverage is good on all the public method inside the tested class, the privates methods called by the public one will be automatically tested since you will assert all the possible case.

The JUnit Doc says:

Testing private methods may be an indication that those methods should be moved into another class to promote reusability. But if you must... If you are using JDK 1.3 or higher, you can use reflection to subvert the access control mechanism with the aid of the PrivilegedAccessor. For details on how to use it, read this article.

Answer 3

Consider using interfaces to expose the API methods, using factories or DI to publish the objects so the consumers know them only by the interface. The interface describes the published API. That way you can make whatever you want public on the implementation objects and the consumers of them see only those methods exposed through the interface.

Answer 4

Okay, so here we have two things that are being mixed. First thing, is when you need to mark something to be used only on test, which I agree with @JB Nizet, using the guava annotation would be good.

A different thing, is to test private methods. Why should you test private methods from the outside? I mean.. You should be able to test the object by their public methods, and at the end that its behavior. At least, that we are doing and trying to teach to junior developers, that always try to test private methods (as a good practice).

Answer 5

Or you can extract this method to some strategy object. In this case you can easily test extracted class and don't make method public or some magic with reflection/bytecode.

Answer 6

We recently released a library that helps a lot to access private fields, methods and inner classes through reflection : BoundBox

For a class like

public class Outer {
    private static class Inner {
        private int foo() {return 2;}
    }
}

It provides a syntax like :

Outer outer = new Outer();
Object inner = BoundBoxOfOuter.boundBox_new_Inner();
new BoundBoxOfOuter.BoundBoxOfInner(inner).foo();

The only thing you have to do to create the BoundBox class is to write @BoundBox(boundClass=Outer.class) and the BoundBoxOfOuter class will be instantly generated.