WS-601: addresses bug in additional_metadata section of image manifest
This MR addresses bug in additional_metadata section of manifest that has a class repr
rather than a JSON-serializable value
-
tests dump all JSON strings; if dumps succeed, the JSON is good -
removed contrived test case -
added test case based on what an image ingestion staging dir is likely to contain
TODO next MR: implement additional tests for new image ingestion test case