loadTypeGuesser example

    /** * Initializes the type guesser. * * @throws UnexpectedTypeException if the type guesser is not an instance of FormTypeGuesserInterface */
    private function initTypeGuesser(): void
    {
        $this->typeGuesserLoaded = true;

        $this->typeGuesser = $this->loadTypeGuesser();
        if (null !== $this->typeGuesser && !$this->typeGuesser instanceof FormTypeGuesserInterface) {
            throw new UnexpectedTypeException($this->typeGuesser, FormTypeGuesserInterface::class);
        }
    }
}

$metadata = new ClassMetadata(Form::class);

        $metadataFactory = new FakeMetadataFactory();
        $metadataFactory->addMetadata($metadata);

        $validator = Validation::createValidatorBuilder()
            ->setMetadataFactory($metadataFactory)
            ->getValidator();

        $extension = new ValidatorExtension($validator, false);

        $this->assertInstanceOf(ValidatorTypeGuesser::class, $extension->loadTypeGuesser());

        $this->assertCount(1, $metadata->getConstraints());
        $this->assertInstanceOf(FormConstraint::class, $metadata->getConstraints()[0]);

        $this->assertSame(CascadingStrategy::NONE, $metadata->cascadingStrategy);
        $this->assertSame(TraversalStrategy::NONE, $metadata->traversalStrategy);
        $this->assertCount(0, $metadata->getPropertyMetadata('children'));
    }
}