PHP で単体テストを行うにはどうすればよいですか?

composer require --dev phpunit/phpunit

class SomeClassTest extends PHPUnit\Framework\TestCase
{
    // ...
}

public function testAddNumbers()
{
    $result = someFunction(1, 2);
    $this->assertEquals(3, $result);
}

vendor/bin/phpunit

class StringUtilsTest extends PHPUnit\Framework\TestCase
{
    public function testUcfirst()
    {
        $string = 'hello world';
        $result = StringUtils::ucfirst($string);
        $this->assertEquals('Hello world', $result);
    }
}

class HttpServiceTest extends TestCase
{
    public function testGetRequest()
    {
        $request = $this->getMockBuilder(HttpRequest::class)
            ->onlyMethods(['get'])
            ->getMock();

        $request->method('get')
            ->with('name')
            ->willReturn('John Doe');

        $service = new HttpService($request);

        $this->assertEquals('John Doe', $service->getRequest('name'));
    }
}