Magento\Catalog\Model\Category\AttributeRepository does not fulfill its service contract

[schmengler]

Preconditions

1. Magento 2.1.0 ans seems still actual for 2.4-develop

Steps to reproduce

1. Write an integration test case as follows:

public function testCategoryAttributeExists($attributeCode)
{
    $categoryAttributesRepository = \Magento\TestFramework\ObjectManager::getInstance()->get(
        \Magento\Catalog\Api\CategoryAttributeRepositoryInterface::class
    );
    $this->assertInstanceOf(
        \Magento\Catalog\Api\Data\CategoryAttributeInterface::class,
        $categoryAttributesRepository->get($attributeCode)
    );
}

1. Pass an existing attribute code via data provider
2. Run the test

Expected result

1. The test passes, because the contract of Magento\Catalog\Api\CategoryAttributeRepositoryInterface states:

    /**
     * Retrieve specific attribute
     *
     * @param string $attributeCode
     * @return \Magento\Catalog\Api\Data\CategoryAttributeInterface
     */
    public function get($attributeCode);

Actual result

1. The test fails with a message like this

Failed asserting that Magento\Catalog\Model\ResourceModel\Eav\Attribute\Interceptor Object (...) is an instance of interface "Magento\Catalog\Api\Data\CategoryAttributeInterface".

[magento-engcom-team]

@schmengler, thank you for your report.
We've created internal ticket(s) MAGETWO-82337 to track progress on the issue.