on Order API test, pass parameters required to create line items, not line items
The idea of the order api is to provide a wrapper around creating a contribution and all of the line item objects, eg the membership created when buying a membership, or the event registration when buying a ticket.
In the specification (https://wiki.civicrm.org/confluence/display/CRM/Order+API), the idea was that there would be array of of the parameters required to create line items. Note that although the entity_table is specified, the entity_id is set to null. Moreover, there is no contribution_id value. Calling the Order API is NOT supposed to require prior calls to create other objects.