編寫單元測試時，一個關(guān)鍵挑戰(zhàn)是確保您的測試專注于被測代碼，而不受外部系統(tǒng)或依賴項的干擾。這就是模擬對象在PHPUnit中發(fā)揮作用的地方。它們允許您以受控方式模擬真實對象的行為，使您的測試更可靠且更易于維護。在本文中，我們將探討什么是模擬對象、它們?yōu)楹斡杏靡约叭绾卧?PHPUnit 中有效地使用它們。

什么是模擬對象？

模擬對象是在單元測試中使用的真實對象的模擬版本。它們允許您：

• 隔離被測代碼：模擬對象模擬依賴關(guān)系的行為，確保測試結(jié)果不受這些依賴關(guān)系實際實現(xiàn)的影響。
• 控制依賴行為：您可以指定調(diào)用某些方法時模擬應(yīng)如何表現(xiàn)，使您能夠測試不同的場景。
• 驗證交互：模擬跟蹤方法調(diào)用及其參數(shù)，確保被測試的代碼與其依賴項正確交互。

為什么使用模擬對象？

模擬在以下場景中特別有用：

• 復(fù)雜的依賴關(guān)系：如果您的代碼依賴于數(shù)據(jù)庫、API 或第三方服務(wù)等外部系統(tǒng)，模擬對象可以通過消除與這些系統(tǒng)交互的需要來簡化測試。
• 交互測試：模擬允許您驗證是否使用正確的參數(shù)調(diào)用特定方法，確保您的代碼按預(yù)期運行。
• 更快的測試執(zhí)行：數(shù)據(jù)庫查詢或 API 請求等實際操作可能會減慢測試速度。模擬這些依賴項可確保更快的測試執(zhí)行。

存根與模擬：有什么區(qū)別？

使用模擬對象時，您會遇到兩個術(shù)語：stubbing 和 mocking:

• 存根：指在模擬對象上定義方法的行為，例如指示方法返回特定值。
• 模擬：涉及設(shè)置對如何調(diào)用方法的期望，例如驗證方法調(diào)用的數(shù)量及其參數(shù)。

如何在 PHPUnit 中創(chuàng)建和使用模擬對象

PHPUnit 通過 createMock() 方法可以輕松創(chuàng)建和使用模擬對象。下面是一些示例，演示了如何有效地使用模擬對象。

示例 1：基本模擬對象用法

在此示例中，我們?yōu)轭愐蕾図梽?chuàng)建一個模擬對象并指定其行為。

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：

• createMock(SomeClass::class) 為 SomeClass 創(chuàng)建一個模擬對象。
• method('someMethod')->willReturn('mocked value') 定義模擬的行為。
• 模擬對象被傳遞給正在測試的類，確保不使用真正的 SomeClass 實現(xiàn)。

示例 2：驗證方法調(diào)用

有時，您需要驗證是否使用正確的參數(shù)調(diào)用了方法。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();
}

要點：

• Expects($this->once()) 確保 someMethod 被調(diào)用一次。
• with($this->equalTo('expected argument')) 驗證是否使用正確的參數(shù)調(diào)用該方法。

示例：使用 PaymentProcessor 進行測試

為了演示模擬對象的實際應(yīng)用，我們以依賴于外部 PaymentGateway 接口的 PaymentProcessor 類為例。我們想要測試 PaymentProcessor 的 processPayment 方法，而不依賴于 PaymentGateway 的實際實現(xiàn)。

這是 PaymentProcessor 類：

class PaymentProcessor
{
    private $gateway;

    public function __construct(PaymentGateway $gateway)
    {
        $this->gateway = $gateway;
    }

    public function processPayment(float $amount): bool
    {
        return $this->gateway->charge($amount);
    }
}

現(xiàn)在，我們可以為 PaymentGateway 創(chuàng)建一個模擬來測試 processPayment 方法，而無需與實際的支付網(wǎng)關(guān)交互。

使用模擬對象測試 PaymentProcessor

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));
    }
}

測試分解：

• createMock(PaymentGateway::class) creates a mock object simulating the PaymentGateway interface.
• method('charge')->with(100.0)->willReturn(true) specifies that when the charge method is called with 100.0 as an argument, it should return true.
• The mock object is passed to the PaymentProcessor class, allowing you to test processPayment without relying on a real payment gateway.

Verifying Interactions

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.

Example: Testing with a Repository

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));
    }
}

Best Practices for Using Mocks

1. Use Mocks Only When Necessary: Mocks are useful for isolating code, but overuse can make tests hard to understand. Only mock dependencies that are necessary for the test.
2. Focus on Behavior, Not Implementation: Mocks should help test the behavior of your code, not the specific implementation details of dependencies.
3. Avoid Mocking Too Many Dependencies: If a class requires many mocked dependencies, it might be a sign that the class has too many responsibilities. Refactor if needed.
4. Verify Interactions Sparingly: Avoid over-verifying method calls unless essential to the test.

Conclusion

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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