Autoloader unit test - first attempt

Question

I am learning TDD and I want to test my AutoLoader class, what needs to do the next job:

• do a check is the namespace is string
• do a check, is the path to directory parameter is a string
• do a check is the path to directory what I want to load is exists, directory and readable.

There will be more jobs, but I am newbee, so I need your opinion about my test:

<?php

namespace Myframework\Application\Autoloader;

class Autoloader {

    /**
     * @var string
     */
    protected $namespace;

    /**
     * @var string
     */
    protected $path;

    public function __construct($namespace, $pathToClassesDirectory = '') {
        if (!is_string($namespace)) {
            throw new \Exception('Namespace must be string');
        }
        if (!is_string($pathToClassesDirectory)) {
            throw new \Exception('Path to directory parameter should be string');
        }
        if (!file_exists($pathToClassesDirectory) || !is_dir($pathToClassesDirectory) || !is_readable($pathToClassesDirectory)) {
            throw new \Exception('Path to directory is not accessible to read: "' . $pathToClassesDirectory . '"');
        }
        $this->namespace = $namespace;
        $this->path = $pathToClassesDirectory;
    }

}

The class:

    <?php

use PHPUnit\Framework\TestCase;

/**
 * @author vaso
 */
require_once '../system/Application/Autoloader/Autoloader.php';

class AutoloaderTest extends TestCase {

    protected $Autoloader;

    public function setUp() {
        $this->Autoloader = new Myframework\Application\Autoloader\Autoloader(TEST_NAMESPACE, BASE_PATH);
    }

    public function tearDown() {
        unset($this->Autoloader);
    }

    public function testConstructorCall() {
        new Myframework\Application\Autoloader\Autoloader('nameSpaceAsString', BASE_PATH);
    }

    public function testConstructorCallNameSpaceIsNotStringException() {
        $this->expectException('Exception');
        new Myframework\Application\Autoloader\Autoloader(2);
    }

    public function testConstructorCallPathIsNotStringException() {
        $this->expectException('Exception');
        $notStringForPath = new stdClass();
        new Myframework\Application\Autoloader\Autoloader(TEST_NAMESPACE, $notStringForPath);
    }

    public function testIsDirectoryExistsException() {
        $this->expectException('Exception');
        new Myframework\Application\Autoloader\Autoloader('x', 'Failed directory what not exist');
    }

}

Test passed, and my methods are works, I am happy. But I doubt this is not how TDD works even if I follow every requirements.

My questions are:

• Is it ok to use constants in test what comes from bootstrap.php to define path?
• All of the test ok, but is this the right way to test a constructor? I feel no for some reason, if its ok, please tell me, if not, please tell me why.

I found a lot of resources about TDD, videos, books, but testing the constructor is not in it.

Answer 1

After some research, I've got these answers:

Testing constructor is totally unnecessary if you follow this: Constructor does Real Work. Unit test for units. The constructor only job is to build the object, nothing else, no new objects creation, no initializing, etc...

For constants: I see no reason why do not use constants (for example for a path) to help me to access my classes for tests.