編寫單元測試時，一個關鍵挑戰是確保您的測試專注於被測程式碼，而不受外部系統或依賴項的干擾。這就是模擬物件在PHPUnit中發揮作用的地方。它們允許您以受控方式模擬真實物件的行為，使您的測試更可靠且更易於維護。在本文中，我們將探討什麼是模擬物件、它們為何有用以及如何在 PHPUnit 中有效地使用它們。
模擬物件是在單元測試中使用的真實物件的模擬版本。它們允許您：
模擬在以下場景特別有用：
使用模擬物件時，您會遇到兩個術語：stubbing 和 mocking:
PHPUnit 透過 createMock() 方法可以輕鬆建立和使用模擬物件。以下是一些範例，示範如何有效地使用模擬物件。
在此範例中，我們為類別依賴項建立一個模擬物件並指定其行為。
use PHPUnit\Framework\TestCase;
class MyTest extends TestCase
{
public function testMockExample()
{
// Create a mock for the SomeClass dependency
$mock = $this->createMock(SomeClass::class);
// Specify that when the someMethod method is called, it returns 'mocked value'
$mock->method('someMethod')
->willReturn('mocked value');
// Pass the mock object to the class under test
$unitUnderTest = new ClassUnderTest($mock);
// Perform the action and assert that the result matches the expected value
$result = $unitUnderTest->performAction();
$this->assertEquals('expected result', $result);
}
}
說明：
有時，您需要驗證是否使用正確的參數呼叫了方法。具體方法如下：
public function testMethodCallVerification()
{
// Create a mock object
$mock = $this->createMock(SomeClass::class);
// Expect the someMethod to be called once with 'expected argument'
$mock->expects($this->once())
->method('someMethod')
->with($this->equalTo('expected argument'))
->willReturn('mocked value');
// Pass the mock to the class under test
$unitUnderTest = new ClassUnderTest($mock);
// Perform an action that calls the mock's method
$unitUnderTest->performAction();
}
重點：
為了示範模擬物件的實際應用，我們以依賴外部 PaymentGateway 介面的 PaymentProcessor 類別為例。我們想要測試 PaymentProcessor 的 processPayment 方法，而不依賴 PaymentGateway 的實際實作。
這是 PaymentProcessor 類別：
class PaymentProcessor
{
private $gateway;
public function __construct(PaymentGateway $gateway)
{
$this->gateway = $gateway;
}
public function processPayment(float $amount): bool
{
return $this->gateway->charge($amount);
}
}
現在，我們可以為 PaymentGateway 建立一個模擬來測試 processPayment 方法，而無需與實際的支付網關互動。
use PHPUnit\Framework\TestCase;
class PaymentProcessorTest extends TestCase
{
public function testProcessPayment()
{
// Create a mock object for the PaymentGateway interface
$gatewayMock = $this->createMock(PaymentGateway::class);
// Define the expected behavior of the mock
$gatewayMock->method('charge')
->with(100.0)
->willReturn(true);
// Inject the mock into the PaymentProcessor
$paymentProcessor = new PaymentProcessor($gatewayMock);
// Assert that processPayment returns true
$this->assertTrue($paymentProcessor->processPayment(100.0));
}
}
檢定分解：
You can also verify that the charge method is called exactly once when processing a payment:
public function testProcessPaymentCallsCharge()
{
$gatewayMock = $this->createMock(PaymentGateway::class);
// Expect the charge method to be called once with the argument 100.0
$gatewayMock->expects($this->once())
->method('charge')
->with(100.0)
->willReturn(true);
$paymentProcessor = new PaymentProcessor($gatewayMock);
$paymentProcessor->processPayment(100.0);
}
In this example, expects($this->once()) ensures that the charge method is called exactly once. If the method is not called, or called more than once, the test will fail.
Let’s assume you have a UserService class that depends on a UserRepository to fetch user data. To test UserService in isolation, you can mock the UserRepository.
class UserService
{
private $repository;
public function __construct(UserRepository $repository)
{
$this->repository = $repository;
}
public function getUserName($id)
{
$user = $this->repository->find($id);
return $user->name;
}
}
To test this class, we can mock the repository:
use PHPUnit\Framework\TestCase;
class UserServiceTest extends TestCase
{
public function testGetUserName()
{
// Create a mock for the UserRepository
$mockRepo = $this->createMock(UserRepository::class);
// Define that the find method should return a user object with a predefined name
$mockRepo->method('find')
->willReturn((object) ['name' => 'John Doe']);
// Instantiate the UserService with the mock repository
$service = new UserService($mockRepo);
// Assert that the getUserName method returns 'John Doe'
$this->assertEquals('John Doe', $service->getUserName(1));
}
}
Mock objects are invaluable tools for writing unit tests in PHPUnit. They allow you to isolate your code from external dependencies, ensuring that your tests are faster, more reliable, and easier to maintain. Mock objects also help verify interactions between the code under test and its dependencies, ensuring that your code behaves correctly in various scenarios
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