5 Ways to Extract Value from Overmocked Tests

2024-11-05

The legacy projects we work with are often flooded with mocks. I already wrote How to Remove Dead Mock Calls from PHPUnit Tests, which focuses on dealing with PHPUnit bloated syntax.

Today, we look at the next wave of improvements that make tests more valuable, more accessible to upgrade and read, and even avoid false types.

Mocking is helpful if you want to unit test a method that depends on complex external factors. Like database response, GPT API response, AWS file storage, etc.

Mocking is also one of the main factors that make upgrading tests prolonged and expensive. During Rector upgrades, we often get to a project that has 300+ test classes that use mocks for project classes.

We want to give mocked objects PHP 7.0 types and have Rector and PHPStan on our back. How do we avoid manual work and maintenance?

I'll share our approach to get the most out of mocks, drop dead code, and make tests more valuable.

Our goals

get as much native PHP code as possible so IDE, Rector, and PHPStan can check it easily
remove any unnecessary dependency on the mocking framework, so any PHP developer can read code
make test fun to work with, not a burden that we have to update with every change of native code

Read the following examples with your mocking tool in mind. Not just PHPUnit but also Prophecy, Phpspec, Mockery, and so on. The syntax sugar of these tools is different, but the principles are the same.

1. A test case where every Property is a Mock

Let's start with a simple question: what does this test case verify?

use PHPUnit\Framework\TestCase;

final class SomeTest extends TestCase
{
    private MockObject $apiClientMock;

    private MockObject $responseMock;

    protected function setUp(): void
    {
        $this->apiClientMock = $this->createMock(ApiClient::class);
        $this->responseMock = $this->createMock(Response::class);
    }

    public function testApiClient(): void
    {
        $this->apiClientMock->expects($this->once())
            ->method('get')
            ->willReturn($this->responseMock);

        $returnedResponse = $this->apiClientMock->get();
        $this->assertSame($this->responseMock, $returnedResponse);
    }
}

Does it verify that the ApiClient::get() method returns the Response object? What if we change the get method body? Nothing will happen because this test only checks that our mocking framework works.

❌

This test case doesn't test our code at all because it overrides our code with made-up behavior. It's like reading a news headline about "thousands of dead" before learning it's only a prediction if we get hit by a meteorite in a movie.

Rule of Thumb 👍

Every single test case should have at least
1 real object that is being tested.

There is a PHPStan rule to discover these.

Add the PHPStan rule, spot those classes, and ensure the expected service is tested.

2. Global Mock Property That is Never Modified

The first rule demands some manual work and care. So we'll take a rest with the next one - an easy pick to make our tests more readable.

I've just used this approach to remove 1000 lines from tests in a couple of seconds:

What is the use case?

use PHPUnit\Framework\TestCase;
use PHPUnit\Framework\MockObject\MockObject;

final class SmarterTest extends TestCase
{
    private TestedService $testedService;

    private MockObject $databaseMock;

    protected function setUp(): void
    {
        $this->databaseMock = $this->createMock(Database::class);
        $this->testedService = new TestedService($this->databaseMock);
    }

    public function test(): void
    {
        $result = $this->testedService->count(1, 3);
        $this->assertSame(3, $result);
    }
}

It has nothing to do with mocking, but it's a visual clutter that makes code more challenging to read and more expensive to maintain.

Can you spot it?

Yes, the $databaseMock Property is only written, but never used later. We can refactor it to a direct variable in the setUp() method:

 use PHPUnit\Framework\TestCase;
 use PHPUnit\Framework\MockObject\MockObject;

 final class SmarterTest extends TestCase
 {
-    private TestedService $testedService;

     private MockObject $databaseMock;

     protected function setUp(): void
     {
-        $this->databaseMock = $this->createMock(Database::class);
+        $databaseMock = $this->createMock(Database::class);
-        $this->testedService = new TestedService($this->databaseMock);
+        $this->testedService = new TestedService($databaseMock);
     }

     public function test(): void
     {
         $result = $this->testedService->count(1, 3);
         $this->assertSame(3, $result);
     }
 }

We use a Rector rule to handle this for us.

3. Use a single Mocking tool

The next step may be advanced, but it's worth the work. In PHP projects developed during PHPUnit 4-9 (2014-2020), we can see 2+ different mocking frameworks. Not rarely.

PHPUnit didn't have a decent way to mock objects at the start. So, PhpSpec was integrated into PHPUnit. As time went by, PHPUnit improved mocking features and eventually removes in-house support for PhpSpec in PHPUnit 9.

That's why test upgrades can lead to exponentially expensive processes. Instead of upgrading PHPUnit, we have to upgrade Prophecy and Mockery at the same time.

That is a waste of time and mental energy.

Rule of Thumb 👍

Pick a single testing framework you like
and drop the rest.

 {
     "require-dev": {
-        "phpspec/prophecy": "*",
-        "mockery/mockery": "*",
         "phpunit/phpunit": "*"
     }
 }

I wrote about PhpSpec to PHPUnit migration in a separate post. To automate most of it, you can use this secret standalone Rector set.

4. Either mock or a Real service

What type is a mocked object? That is the question.

If we mock a Product class, it will become:

a) Product|MockObject
b) Product&MockObject
c) MockObject
d) Product

The technical answer is b) because a new proxy mock object will extend MockObject, which will extend Product.

But how does it help IDE, Rector, and PHPStan?

$productMock = $this->createMock(Product::class);

Do we need to call actual methods on mock directly?

$productMock->getName();

No, we set mocks and pass mocks object into the real object we test:

$productMock->expects($this->once())
    ->method('getName')
    ->willReturn('Wifi Router');

$productRepository = new ProductRepository([$productMock]);

If IDE autocompletes $product->getName(), it might lead us astray as the object is a real Product object. We want to avoid ambiguity and separate MockObject properties from real classes.

To add fuel to the fire, PHPStan fails to resolve type if tested Product class is final.

Separate `MockObjects and real classes to give our tests clarity:

-private MockObject|Product $product;
+private MockObject $product;

-private MockObject|ProductRepository $productRepository;
+private ProductRepository $productRepository;

-private MockObject|Database $database;
+private MockObject $database;

Now we see right from the properties which object is being tested.

We use a Rector rule to handle this.

5. Use Entity Objects Directly

Last but not least is the mocking of simple objects. Let me give you an example:

use PHPUnit\Framework\TestCase;

final class ProductRepositoryTest extends TestCase
{
    public function test(): void
    {
        $productRepository = new ProductRepository();

        $productMock = $this->createMock(Product::class);
        $productMock->method('getName')
            ->willReturn('Latest PHP conference talk');

        $productRepository->save($productMock);

        // ...
    }
}

Let's recall one of our goals defined at the start of this post:

remove any unnecessary dependency on the mocking framework, so any PHP developer can read code

What can be improved there? We can use the Product object directly:

 use PHPUnit\Framework\TestCase;

 final class ProductRepositoryTest extends TestCase
 {
     public function test(): void
     {
         $productRepository = new ProductRepository();

-        $productMock = $this->createMock(Product::class);
+        $product = new Product();
-        $productMock->method('getName')
-             ->willReturn('Latest PHP conference talk');
+        $product->setName('Latest PHP conference talk');

         $productRepository->save($productMock);

         // ...
     }
 }

This code is more intuitive to read and cheaper to maintain:

we have type control on getName() input
if we change the method in the future, IDE will update it here as well

But how do we know we can replace the mock with a real object here? What if we have another mock line like:

       $resolverMock = $this->createMock(ComplicatedProductNameResolver::class);
       $resolverMock->method('getName')
            ->willReturn('Latest PHP conference talk');

This is clearly a service, but Product is an entity. How do we know that?

It has a marker. Doctrine ORM/ODM entities have an annotation or a PHP 8.0 attribute:

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity()
  */
class Product
{
}

Rule of Thumb 👍

Never mock Doctrine ORM/ODM entities.
Use them directly.

We use PHPUnit Rector rule to handle this case.

That's all for today. Get PHPStan and Rector rules on board, and let them work for you. There is more than meets the eye when it comes to mocks. We'll tackle automated refactoring of simple services in the next part.

Happy coding!

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