it happened to me two years ago and im still so upset about it.  ive smoked weed maybe 4 times and havent in 10 years.  the guy giving me the exam tried to relate to me and said it was obvious i was lying and that because ive worked in restaurants most my career i probably did something after work.  he also said that it wasnt just about drug use but that i lied about my past history of drugs, implying that i dealt.  i worked very hard to get to that test, physically, emotionally, mentally, and i was so happy after completing every step and to have it all taken away on a test is deflating.  the border patrol is something i believe in, and i wanted to be an agent so badly that to not even be granted a second chance to take the test...quite painful