Hair drug tests?? 2 part question?

In May I took a trip to Seattle. I d never smoked before I figured since it was legal, it d be alright. I had one joint that was a gram and a small cookie that I m guessing was probably 10Mg (don t really remember) After trying both of those (not together) I didn t feel a thing. I mainly attribute to being overweight. Fast forward to today. I just had a interview and he mentioned about doing a hair test. I don t have much hair on my head. I keep it around 1/4 inch. I do have a decently sized beard that they might be able to take a sample from. So I basically have 2 questions. #1 could being a one event user 5 months ago that didn t even feel any effects fail a hair test? And #2 would most places test facial hair as a sample if that s their only option?