How come 2 inserts with same PK succeed? How can I update a duplicate key?

I have an application which from what I understand uses SQLiteDatabase.
I see that 2 insert of the same data (same PK) do not seem to fail.

Uri res = context.getContentResolver().insert(CONTENT_URI, values);
res = context.getContentResolver().insert(CONTENT_URI, values);  

So whe I print res I see:

http://contentapplication_id/my_table_name/10  
http://contentapplication_id/my_table_name/11 

Does this mean that the row was inserted 2 times with ids 10 & 11?

But how is that possible if I am inserting 2 rows with the same id?
How can I verify what is happening?
My actual problem: I am interested in doing something like on duplicate PK update and noticed this