annotation to make a private method public only for test classes

Question

Who has a solution for that common need   I have a class in my application   some methods are public  as they are part of the api  and some are private  as they for internal use of making the internal flow more readable  now  say I want to write a unit test  or more like an integration test  which will be located in a different package  which will be allowed to call this method  BUT  I want that normal calling to this method will not be allowed if you try to call it from classes of the application itself  so  I was thinking about something like that  public class MyClass       public void somePublicMethod                        PublicForTests    private void somePrivateMethod                       The annotation above will mark the private method as  public for tests  which means  that compilation and runtime will be allowed for any class which is under the test    package   while compilation and or runtime will fail for any class which is not under the test package   any thoughts  is there an annotation like this  is there a better way to do this   it seems that the more unit tests you write  to more your inforced to break your encapsulation

User · Answer

As much as I know there is no annotation like this. The best way is to use reflection as some of the others suggested. Look at this post:
How do I test a class that has private methods, fields or inner classes?

You should only watch out on testing the exception outcome of the method. For example: if u expect an IllegalArgumentException, but instead you'll get "null" (Class:java.lang.reflect.InvocationTargetException).
A colegue of mine proposed using the powermock framework for these situations, but I haven't tested it yet, so no idea what exactly it can do. Although I have used the Mockito framework that it is based upon and thats a good framework too (but I think doesn't solve the private method exception issue).

It's a great idea though having the @PublicForTests annotation.

Cheers!

User · Answer

I am not aware of any such annotation  however the following may be of value   unit testing private methods or the following   JMockit

User · Answer

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

User · Answer

An article on Testing Private Methods lays out some approaches to testing private code   using reflection puts extra burden on the programmer to remember if refactoring is done  the strings aren t automatically changed  but I think it s the cleanest approach

User · Answer

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

User · Answer

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

User · Answer

dp4j has what you need  Essentially all you have to do is add dp4j to your classpath and whenever a method annotated with  Test  JUnit s annotation  calls a method that s private it will work  dp4j will inject the required reflection at compile-time   You may also use dp4j s  TestPrivates annotation to be more explicit   If you insist on also annotating your private methods you may use Google s  VisibleForTesting annotation

User · Answer

The common way is to make the private method protected or package-private and to put the unit test for this method in the same package as the class under test  Guava has a  VisibleForTesting annotation  but it s only for documentation purposes

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

I just put the test in the class itself by making it an inner class  https   rogerkeays com how-to-unit-test-private-methods

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

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