I have a Test class which was working fine but after a new process builder was created on user object to update a custom field created on user object, it started failing. In my test class code I am inserting the account, contact and then a user related to that contact, the test is throwing Mixed DML error. I understand that this is because I cant do DML on both setup and non-setup in single transaction,so used Test.startTest and Test.stopTest and within it I inserted the user but it didn't work. For the second option ,i.e, User of System.runAs(user), I cant do this as this "user" is what I am inserting . How to deal and resolve this?