FooSubType example

$resolvedFormType = $this->registry->getType(FooType::class);

        $this->assertInstanceOf(ResolvedFormType::class, $resolvedFormType);
        $this->assertSame($type, $resolvedFormType->getInnerType());
        $this->assertSame([$ext1, $ext2], $resolvedFormType->getTypeExtensions());
    }

    public function testGetTypeConnectsParent()
    {
        $parentType = new FooType();
        $type = new FooSubType();

        $this->extension1->addType($parentType);
        $this->extension2->addType($type);

        $resolvedFormType = $this->registry->getType(FooSubType::class);

        $this->assertInstanceOf(ResolvedFormType::class, $resolvedFormType);
        $this->assertSame($type, $resolvedFormType->getInnerType());

        $resolvedParentFormType = $resolvedFormType->getParent();