There's something I've only been doing since a year or so, and I've come to like it a lot. My previous testing experiences were mostly at the level of unit tests or functional/system tests. What was left out of the equation was integration tests. The perfect example of which is a test that proves that your custom repository class works well with the type of database that you use for the project, and possibly the ORM or database abstraction library you use to talk with that database. A test for a repository can't be a unit test; that wouldn't make sense. You'd leave a lot of assumptions untested. So, no mocking is allowed.

But how do you test everything that is going on in a repository? Well, I found out a nice way of doing so, one that even allows you to use some kind of test-driven approach. In this article I'll cover one of the two main use cases for repositories: querying the database, and returning some objects for it. The other use case - storing and loading objects - will be discussed in another article.

When you're looking at a function (an actual function or a method), you can usually identify several blocks of code in there. There are pre-conditions, there's the function body, and there may be post-conditions. The pre-conditions are there to verify that the function can safely proceed to do its real job. Post-conditions may be there to verify that you're going to give something back to the caller that will make sense to them.

In a quasi-mathematical way: most pre-conditions verify that the input is within the supported domain of the function. Post-conditions verify that the output is within the range of the function. A mathematical function (as far as I know) only verifies its pre-conditions, because bad input could've been provided for which the function just doesn't work (e.g. 1/x doesn't work for input x = 0). Once the input has been validated, the function will yield an answer which doesn't have to be verified. Every answer will be valid no matter what.

I recently wrote about when to add an interface to a class. After explaining good reasons for adding an interface, I claim that if none of those reasons apply in your situation, you should just use a class and declare it "final".

PHP 5 introduces the final keyword, which prevents child classes from overriding a method by prefixing the definition with final. If the class itself is being defined final then it cannot be extended.

— PHP Manual, "Final Keyword"

An illustration of the final syntax for class declarations:

final class CanNotBeExtended
{
    // ...
}

class CanStillBeExtended
{
     // ...
}

class Subclass extends CanStillBeExtended
{
    // override methods here
}

// Produces a Fatal error:

class Subclass extends CanNotBeExtended
{
    // ...
}

For a couple of years now I've been using the final keyword everywhere (thanks to Marco Pivetta for getting me on track!). When I see a class that's not final, it feels to me like it's a very vulnerable class. Its internals are out in the open; people can do with it what they want, not only what its creator has imagined.

Still, I also remember my initial resistance to adding final to every class definition, and I often have to defend myself during workshops, so I thought it would help if I explained all about it here.