Mocking parcial

I was about to say the same thing. I ran into issues when trying to manually set a service in the container during testing. I believe it might happen more often in cases when only one (or any subset) of your tests in a class need to override the service.

I was using the happyr/service-mocking package for a while, but ran into issues regarding services that use the same class, but have different configurations. In my case the affected services were different Flysystem storages.

One possible solution might be to create a proxy (partial mock that falls back to real implementation) service, set it in the container during test setup, and then override the method behavior on it as needed. You can create a proxy with by calling $this->createTestProxy($className, $constructorArguments) in PHPUnit, where $className is the class you want to proxy, and $constructorArguments is an array of arguments to pass in the construction of the specified class. I haven't seen this proxy method used often in documentation, blog posts, or SA questions I've looked at in my search for an alternative solution to the problem happyr/service-mocking addresses. I'm not sure why that is the case, because using proxy objects has helped me a lot in writing tests at work.

Here is a possible example:
EDIT 2: Regarding Edit 1... According to the documentation overriding private services should work for Symfony 6.x or 7.x. I'm using 5.4, which does not seem to support this.

EDIT 1: After testing, I've found this specific example doesn't work because you can't overwrite a private service and the upload.storage service would be private with the default Flysystem config. It seems like this should be something that is allowed in the KernelTestCase class since you are allowed to retrieve private services even though that is normally prohibited in non-test code. So, this example would work, but only if the service you are replacing is public :/ My real-world work around currently is just making the proxy object and then manually constructing the depending service (UploadManager in this example), passing in the proxy object and retrieving services from the container as needed.

use Symfony\Bundle\FrameworkBundle\Test\KernelTestCase;
use League\Flysystem\Filesystem;
use League\Flysystem\InMemory\InMemoryFilesystemAdapter;
use League\Flysystem\UnableToWriteFile;
use Symfony\Component\HttpFoundation\File\UploadedFile;
use App\Service\Uploader;
use App\Exception\UploadException;
// ...other imports...

class UploaderTest extends KernelTestCase 
{
    private Uploader $uploader;
    
    protected function setUp(): void
    {
        // create a proxy for the service we want partially modify behavior for
        $uploadStorageProxy = $this->createTestProxy(Filesystem::class, [new InMemoryFilesystemAdapter]);
    
        self::bootKernel();
        
        // call this before getting services from the container that depend on 'upload.storage'
        // THIS ONLY WORKS IF THE SERVICE IS PUBLIC
        self::getContainer()->set('upload.storage', $uploadStorageProxy);
    
        // make the service we are testing in this easily accessible for all tests
        // this service depends on the 'upload.storage' service
        $this->uploader = self::getContainer()->get(Uploader::class);
    }
    
    // ...several tests that don't need to modify 'upload.storage' service behavior
    
    public function testUploadExceptionThrownWhenStoringFileFails(): void
    {
        // get proxied service
        $uploadStorage = self::getContainer()->get('upload.storage');
        
        // modify desired method of proxied service and make sure it is called
        $uploadStorage
            ->expect($this->once())
            ->method('writeStream')
            ->willThrowException(new UnableToWriteFile());
            
        // making sure some custom exception is thrown
        $this->expectException(UploadException::class);
        
        $this->uploader->upload($this->createTestFile);
    }
    
    private function createTestFile(): UploadedFile
    {
        // create and return a basic UploadedFile object for testing
    }
}

Ok, so it turns out the functionality to create a test proxy (and it's supporting methods) are being deprecated. So... I guess this isn't the way to go :( According to this issue it is being deprecated solely for the fact that the author hasn't seen it used much?

Thanks for the details Joe! My mission this year is to improve the Symfony testing process experience and this is one area that needs improvement.

Hey Kevin!

Excellent point - I was not aware of that library, it seems great. By the way, if your tests are not very complex, you can create a services_test.yaml file and override any service definition that you may need on your functional tests

Cheers!