Suppose the following scenario:

  • I have a class that makes calls to an external service
  • The class implements an interface and is defined as preferred implementation for this interface in di.xml
  • A block receives this interface as constructor parameter
  • I want to test a Magento request in an integration test that uses this block

I don't want to actually call the external service, so I would like to mock that class and wonder what's the best way to do so.

I know that you can define DI preferences on the fly with

    ['preferences' => [TheInterface::class => MockClass::class]]

but this requires defining a mock class MockClass yourself, I cannot use a PHPUnit mock object.

This works okay if the injected class is a factory because I can create a mock factory that creates the actual mock object.

But is this the only way or am I missing something?


The suggested method

$objectManager->addSharedInstance($mock, TheInterface::class);

looked good first, but only worked as long as there were no preferences defined. These take precedene over shared instances.

I tried to dynamically remove the preference:

    ['preferences' => [TheInterface::class => null]]

But unfortunately Magento calls ltrim($to, '\\') on the argument, which converts it to an empty string. This results in:

ReflectionException: Class does not exist

1 Answer 1


You can use \Magento\TestFramework\ObjectManager::addSharedInstance for this.


$objectManager->addSharedInstance($mock, TheInterface::class);
  • 3
    Works well if there is no preference set yet in di.xml, but the preference seems to have priority over the shared instance. Commented Mar 6, 2016 at 19:01
  • 4
    In this case you need add shared interface for preferred class. for ex. if we have <preference for="Psr\Log\LoggerInterface" type="Magento\Framework\Logger\Monolog" /> than you should add shared instance as $objectManager->addSharedInstance($mock, "Magento\Framework\Logger\Monolog");
    – KAndy
    Commented Mar 6, 2016 at 19:36
  • 1
    Nice, that worked! Commented Mar 6, 2016 at 19:46
  • 3
    Please note that if you want to mock a virtual type, you have to use the name of the virtual type, not the class name: $this->objectManager->addSharedInstance($mockedLogger, 'CustomLogger');. Knowing this would have saved me an hour :-P Commented Jan 28, 2019 at 11:13
  • @GielBerkers You saved me an hour :-) Commented Jun 14 at 12:45

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