Maybe this test is a bit poor. I'd suggest to expand it, considering the following steps:

1. Create and entity with an attribute as preparation step (using the corresponding standard or convenience operation)
2. Update the attribute using the new implemented operation, with type
3. Query to check that the value was updated
4. Update the attribute using the new implemented operation, without type
5. Query to check that the value was updated.

Steps 2 and 3 guarantee that the operation works, with and without type specification in the updateContextAttributeRequest payload.

In addition, I'd include a "parallel" test for the JSON case.