PHP Unit Testing Guide: How to Use Mock Objects to Improve Test Efficiency

Overview of Mock Objects in Unit Testing

Mock objects are commonly used test doubles in unit testing. They simulate the behavior of classes or interfaces while allowing precise control over their return values or exceptions. Using mock objects, developers can test the interaction of functions or methods without instantiating actual dependencies.

Creating Mock Objects

In PHP, you can create mock objects using the getMockBuilder method. This method accepts the following parameters:

• $originalClassName: The name of the class or interface to mock.
• $methods (optional): An array of method names to mock.

// Mock the MyInterface interface
$mock = $this->getMockBuilder(MyInterface::class)
             ->getMock();

// Mock the MyClass class and its methods
$mock = $this->getMockBuilder(MyClass::class)
             ->setMethods(['myMethod'])
             ->getMock();

Configuring Mock Objects

After creating a mock object, you can configure its behavior using the method function to return specific values or throw exceptions:

// Configure mock object to return 'foo'
$mock->method('getMyMethod')
     ->willReturn('foo');

// Configure mock object to throw an exception
$mock->method('myOtherMethod')
     ->willThrowException(new RuntimeException());

Practical Example

Here is an example demonstrating how to use mock objects in unit testing. Suppose we have a MyClass class that depends on a MyService class:

class MyClass
{
    private $myService;

    public function __construct(MyService $myService)
    {
        $this->myService = $myService;
    }

    public function doSomething(): string
    {
        return $this->myService->getData();
    }
}

The MyService class has a getData method that returns the string "foo". To test MyClass::doSomething, you can use a mock object:

class MyClassTest extends PHPUnit_Framework_TestCase
{
    public function testDoSomething()
    {
        // Create a mock object for MyService
        $mockService = $this->getMockBuilder(MyService::class)
                            ->setMethods(['getData'])
                            ->getMock();

        // Configure the mock to return 'bar'
        $mockService->method('getData')
                    ->willReturn('bar');

        // Create an instance of MyClass and inject the mock
        $myClass = new MyClass($mockService);

        // Assert that MyClass::doSomething returns 'bar'
        $this->assertEquals('bar', $myClass->doSomething());
    }
}

In this test, we created a mock object for MyService and set its return value to "bar". Then we injected the mock into an instance of MyClass and asserted that doSomething returned "bar", verifying the correct interaction between MyClass and MyService.

Using mock objects in unit tests allows developers to efficiently verify dependencies and business logic without relying on actual services or complex environments.