I had the exact same problem, even flagging (SeeAllData=false) explicitly. It appears that even in test cases SF validates the SKU across all product records
It appears that even in test cases SF validates the SKU across all product records.
I got around it in my test classes by ensuring the product SKU was guaranteed to be uniqueunique & not match anything in an existingexisting product record (in my case I appended 'SF-UNITTEST-' to all SKUs in my spoofed http requests). Hope this helps someone else who had this problem!