Use JSON for all test requests
Requires !2418 (merged), closes #1829 (closed)
Making the switch showed a bug in CreateElementChildren
: calling it with {"children": []}
did not cause an error as expected. Since the multipart
format does not support lists at all, it sent nothing, so the endpoint interpreted it as a required field being missing rather than a field set to an empty list, so the bug went unnoticed.
I removed all of the format="json"
we were using in the requests to force the format when the multipart
format was causing us trouble, since it is now the default.