DUPLICATE_VALUE error when inserting a deep cloned record

Question

I'm writing a method that has to insert a clone of a given record of Object__c.

I'm obtaining the clone performing a deep clone. That is:

object.clone(false, true, false, false)

The insertion of the clone fails because of “duplicate value found: 'unknown' duplicates value on record with id: 'unknown'” error.

There is a workflow rule that updates the field unique__c to be equal to 'C' + Object__c.Name. And the field unique__c has to be, indeed, unique. If I modify unique__c to not be unique I can insert the clone. Name is non writeable auto number, so I cleared unique__c in the clone before trying to insert it like:

clone.unique__c = null 

But it still gives me the error. Per the workflow rule, I guess the unique__c field is populated with 'C' + the name as expected, but before doing the insert I compare the original object's name and the cloned one's and they differ. The latter is null.

Why can't I insert this clone? I got it clear from the steps above that the problem is the unique__c field so: Why, if I clear it before inserting, do I still get the error? Also, I checked that the Name of the clone is null before inserting so the workflow should not set nothing or set null in unique__c so, how come it gets to interfere with the insert?

PS: This is all being done in a test without seeing all data, so I discarded that there was already a record of Object__c that had unique__c to null.

Answer 1

The problem was that I was creating an Object__c record on a @testSetup method. For some reason I don't understand, the autonumber goes back and repeats values when creating records outside of that @testSetup method. My solution was to drop the testSetup annotation and call the setup method manually. But still I made another question here.