TESTING LEGACY TROUBLES @konrad_126 

LEGACY CODE? NO TESTS. 

THE CASE OF AN IRRITATING PARAMETER 

vatProvider->getRate($product->countryCode()); // some business logic to calculate price } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 public function __construct(private VatDotComClient $vatProvider) vatProvider->getRate($product->countryCode()); 11 // some business logic to calculate price 12 } 13 } 14 $taxRate = $this->vatProvider->getRate($product->countryCode()); vatProvider->getRate($product->countryCode()); 11 12 } 13 } 14 

vatProvider->getRate($product->countryCode()); // some business logic to calculate price } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 public function __construct(private VatDotComClient $vatProvider) vatProvider->getRate($product->countryCode()); 11 // some business logic to calculate price 12 } 13 } 14 

vatProvider->getRate($product->countryCode()); // some business logic to calculate price } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 public function __construct(private VatProvider $vatProvider) vatProvider->getRate($product->countryCode()); 11 // some business logic to calculate price 12 } 13 } 14 

rate; } } 1 2 3 4 5 6 7 8 9 10 11 12 13 class TestProvider implements VatProvider rate; 11 } 12 } 13 public function __construct(private float $rate) rate; 11 } 12 } 13 return $this->rate;

THE CASE HIDDEN DEPENDENCY 

process($payment); // ... Assert stuff } 1 2 3 4 5 6 7 8 9 10 11 

mailer = new Mailer('api-key', 'secret'); // some code } public function process(Payment $payment) { // ... $this->mailer->send( $payment->receiver(), new PaymentNotificationMessage($payment) ); } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 $this->mailer = new Mailer('api-key', 'secret'); mailer->send( 16 $payment->receiver(), 17 new PaymentNotificationMessage($payment) 18 ); 19 20 } 21 } 22 $this->mailer->send( $payment->receiver(), new PaymentNotificationMessage($payment) ); } } mailer = new Mailer('api-key', 'secret'); 8 // some code 9 } 10 11 public function process(Payment $payment) 12 { 13 // ... 14 15 16 17 18 19 20 21 22 

mailer = new Mailer('api-key', 'secret'); } public function process(Payment $payment) { // ... } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 

mailer = $mailer; } public function process(Payment $payment) { // ... } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Parameterize Constructor (Extract Interface) 

DESIGN? 

dependency injection principle strategy design pattern depend on abstract not a concrete 

MORE ADVICE? 

THANK YOU @konrad_126