How to test code that relies on external services or APIs with PHPUnit?

When testing code that relies on external services or APIs, it is important to mock or stub these dependencies to ensure reliable and isolated testing. PHPUnit provides various ways to achieve this:

Mocking: PHPUnit provides a mocking framework that allows you to create mock objects that simulate the behavior of the external service or API. Mock objects can be programmed to return fixed values or simulate specific behavior.

$mock = $this->getMockBuilder(ExternalService::class)
             ->disableOriginalConstructor()
             ->getMock();
$mock->method('someMethod')->willReturn('expectedResult');

Stubbing: PHPUnit also allows you to create stubs, which are objects that implement the same interface as the external service or API but provide predefined responses. Stubs are useful when you want to test specific scenarios.

$stub = $this->getMockBuilder(ExternalService::class)
             ->disableOriginalConstructor()
             ->getMock();
$stub->method('someMethod')->will($this->returnValue('expectedResult'));

Dependency Injection: Instead of directly instantiating and using the external service or API, you can inject them into your tested code as dependencies. This allows you to provide mock objects during testing, which isolates the code under test from the actual external services or APIs.

class MyClass {
    private $externalService;

    public function __construct(ExternalService $externalService) {
        $this->externalService = $externalService;
    }

    public function myMethod() {
        $result = $this->externalService->someMethod();
        // ...
    }
}

// During testing:
$mock = $this->getMockBuilder(ExternalService::class)
             ->disableOriginalConstructor()
             ->getMock();

$myClass = new MyClass($mock);

By using these techniques, you can test your code in isolation without relying on the availability and consistency of external services or APIs, ensuring more reliable and repeatable tests.