Unit Testing Question

[Wardrop]

Apologies for the generic title, but I couldn't really sum this up in a few words.

When writing a Unit Test, the goal is obviously to test the public interface of a class, to ensure it behaves as expected. I have at least one test (method) for each method of a class, but I find when testing a particular method, I usually have to rely on another method of the same class to verify the correct behaviour of the method I'm testing. I generally try to avoid doing this, but often I don't have a choice as many of the classes properties are protected.

What's the general stance on this? Should you avoid using other methods of the same class to verify the correct behaviour of the method your testing, or is it really not a problem?

Here's an example of what I mean just in case the wording is a little confusing...

function testRegisterMethod ()
{
    $obj = new Example;
    $obj->register('test', 'example data');
    $this->assertTrue( $obj->isRegistered('test') );
} 

As you can see in the example above, although I'm trying to test the register() method, I'm really testing both it, and the isRegistered() method. So a failure (or even a pass) of this test, really doesn't indicate what has exactly failed or succeeded.

[Mal Curtis]

If you check to see if the isRegistered works before you register then you can see if change is happening due to the register method.

ie.
if isregistered asserts true before the register -> problem
If isregistered asserts false STILL after the register -> problem.

Unfortunately that is only useful in simplish situations!

[Wardrop]

Yeah that's true. Thanks for the tip. Speaking more generally though, is this generally accepted practice to rely on other methods of the same class for verifying behaviour of a particular method?

[AnthonySterling]

I would say so, you're testing this particular scenario, if either of these methods fail, then the scenario fails.

[Wardrop]

Well yeah, that's what I was thinking, but wasn't sure if this was the norm for unit tests.

[Mal Curtis]

It should be fine - also if it were a more intensive setup / more complex you'd have other unit tests setup for either an individual method or that method amongst others. If it works in one, then a test which it's also in doesn't you can generally assume it's due to other methods.