Question

I have a class that looks something like this:

class Foo {
    protected $_arr = array();

    public function has($key) {
        return array_key_exists($key, $this->_arr);
    }

    public function add($key, $val) {
        $this->_arr[$key] = $val;
    }
}

For my PHPUnit tests for these methods, the only way I can think if to test add() is by asserting that has() returns TRUE for the same key after adding it. This makes my testAdd() test dependent on my testHas() test. Conversely, the only way I can think of to test has() is basically doing the exact same steps, but this would make this test dependent on an already dependent test, producing a chicken and egg type problem.

Am I going about this the wrong way? What’s a better method for testing stuff like this?

Answer 1

Instead of writing one-test-per-method, design your tests around the functionality the class must provide. You’ll have tests that exercise multiple methods, but that’s fine because it indicates to the developer that those methods are related. This is where Test Driven Development–where you write the tests while designing the contract for the class before writing the code for the class–really shines.

class FooTest extends PHPUnit_Framework_TestCase
{
    function testStartsEmpty() {
        $foo = new Foo;
        self::assertFalse($foo->has('bar'));
    }

    function testAddStoresKeys() {
        $foo = new Foo;
        $foo->add('bar', 'baz');
        self::assertTrue($foo->has('bar'));
    }

    function testAddStoresKeysWithNullValues() {
        $foo = new Foo;
        $foo->add('bar', null);
        self::assertTrue($foo->has('bar'));
    }

    function testAddStoresValues() {
        $foo = new Foo;
        $foo->add('bar', 'baz');
        self::assertEquals('baz', $foo->get('bar'));  // fatal error
    }
}

Now that testAddStoresValues() fails, it’s time to implement a method to get the value for a given key: Foo::get($key).