Learn Haxe

Testing Private Code with @:allow and @:access

Posted on 2016-03-28

Tagged with: Haxe

When writing unit tests, you sometimes face the choice of changing class/method/property access to public instead of private to facilitate testing. Sometimes, it can feel like a terrible decision to break the public interface of a class just to make it easier to test.

Fortunately, you don't have to do that. Haxe allows you to annotate classes and methods with two access modifiers:

• @:allow(package.and.class.Name): Allow the class Name in the namespace package.and.class to access this class' private methods and properties.
• @:access(package.and.class.Name): allow this method/class to access package.and.class.Name's private methods and properties. Useful when you can't modify the class you want to test, or it's impractical to give access to all the test classes that need it.

(You can read more about them on the Access Control documentation page.)

A word of caution: this borders on white-box testing (i.e. verifying the implementation works in a specific way) -- which creates fragile tests that require frequent change. I suggest, as much as possible, not to rely on private code for testing.

Instead, rely on some observable, public properties or methods that allow you to indirectly. For example, if you have a Player class in an RPG, you probably can't test the levelUp method directly; instead, you can grant your player lots of experience, and observe that it eventually does level up.