Subject: How to retrieve multiple linked Attachments

We need to check via the SOAP API whether a specific document is linked to more than one test step artifact.. The attachments keep some unique data which is updated from time to time. We do not want to create a new attachment on update.

The somewhat obvious way of iterating over all test cases, then getting all test steps and building a list of attachmentIDs of their attachments is rather cumbersome and time intensive.   Is there a better way to check if a attachment is linked only one TestCase? We would like to use "associationRetrieveForArtifact(...)" method , but regardless of parameters we always receive a null result. Would you be able to provide an example of how to use the above method for the described use case ? Thanks in advance.