Someone will no doubt be able to quote Stds Doc 19 on this but paraphrasing . . .
You cannot take the PPL Skill Test with anyone who has taken any part in your training. However, the examiner is allowed to have carried out 'safety check flights' on you during training.
If we're talking CPL Skill Test then the examiner cannot even be a member of the same Flying Training Organisation (unless you're on an integrated course).