Common problems and solutions in PHP unit testing practice

FAQ in PHP unit testing: External dependency testing: Use a mocking framework (such as Mockery) to create fake dependencies and assert their interactions. Private member testing: Use reflection APIs such as ReflectionMethod to access private members or use test visibility modifiers such as @protected. Database interaction testing: Set up and verify database state using a database testing framework such as DbUnit. External API/Web Service Testing: Use an HTTP client library to simulate interactions, using a local or stub server in the test environment.

Frequently Asked Questions in PHP Unit Testing

Question 1: How to target code with external dependencies unit test?

Solution: Use a mocking framework, such as PHPUnit's Mockery or Prophecy, that allows you to create fake dependency objects and make assertions about their interactions.

use Prophecy\Prophet;

class UserRepoTest extends \PHPUnit\Framework\TestCase
{
    public function testFetchUser(): void
    {
        $prophet = new Prophet();
        $cache = $prophet->prophesize(Cache::class);

        $userRepo = new UserRepo($cache->reveal());

        $actualUser = $userRepo->fetchUser(1);

        $cache->get(1)->shouldHaveBeenCalled();
        $this->assertEquals($expectedUser, $actualUser);
    }
}

Question 2: How to test private methods or properties?

Solution: Use reflection APIs (such as ReflectionClass and ReflectionMethod) that allow you to access private members. However, it can make tests difficult to maintain.

Another solution is to use a test-specific visibility modifier, such as PHPUnit's @protected.

class UserTest extends \PHPUnit\Framework\TestCase
{
    public function testPasswordIsSet(): void
    {
        $user = new User();

        $reflector = new ReflectionClass($user);
        $property = $reflector->getProperty('password');

        $property->setAccessible(true);
        $property->setValue($user, 'secret');

        $this->assertEquals('secret', $user->getPassword());
    }
}

Question 3: How to test database interaction?

Solution: Use a database testing framework, such as PHPUnit's DbUnit or Doctrine DBAL Assertions, that allow you to set and verify database state.

use PHPUnit\DbUnit\TestCase;

class PostRepoTest extends TestCase
{
    protected function getConnection(): Connection
    {
        return $this->createDefaultDBConnection();
    }

    public function testCreatePost(): void
    {
        $dataset = $this->createXMLDataSet(__DIR__ . '/initial-dataset.xml');
        $this->getDatabaseTester()->setDataSet($dataset);
        $this->getDatabaseTester()->onSetUp();

        $post = new Post(['title' => 'My First Post']);
        $postRepo->persist($post);
        $postRepo->flush();

        $this->assertTrue($this->getConnection()->getRowCount('posts') === 1);
    }
}

Question 4: How to test code that relies on external APIs or web services?

Solution: Use an HTTP client library to simulate interactions with external services. In a test environment, you can use a local or stub server.

use GuzzleHttp\Client;

class UserServiceTest extends \PHPUnit\Framework\TestCase
{
    public function testFetchUser(): void
    {
        $httpClient = new Client();
        $userService = new UserService($httpClient);

        $httpClient
            ->shouldReceive('get')
            ->with('/users/1')
            ->andReturn(new Response(200, [], json_encode(['id' => 1, 'name' => 'John Doe'])));

        $user = $userService->fetchUser(1);

        $this->assertInstanceOf(User::class, $user);
        $this->assertEquals(1, $user->getId());
    }
}

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