Should I worry about a drug test? [View All]

[Nikia]

I have applied for and interviewed for a job which I'd like to get. Two weeks ago, I had a first interviewed, last week I had a second interview, and this coming week I have a third interview and psych exam. In the first interview, they told me that this was the interview process. They are flying in the shrink for me and one other candidate, although I was told that I was the top candidate. They never said anything about a drug test although they were upfront about the psych test.
This is a small privately held corporation which I do not wish to name. I do not know anyone who works there that I have not met through the interview process. The people who I know who might know someone who works there, work for my current company and I don't know them well enough to trust them either with the information that I might be leaving the company soon or such a thing might be a concern to me.
They wouldn't fail to disclose that fact, would they if they tested? Should I lay off the pot this weekend anyway?