Will you pass a drug test if you took half an Ecstasy pill two days ago?

You're cutting it super close, but it's possible. MDMA can be traced in your urine for 3-5 days (a statistic based on "average" dosage), and a smaller dose would indeed get out of your system slightly faster. Factors to take into consideration regarding this are your body composition, metabolism, and whether the pill was cut with other chemicals (studies show 70% contain other chemicals).