Can k9 narcotic unit smell small amounts of drugs?

If the drugs are in a concealed bag/envelope on the Suspect, then it is safe, But if, Lets say you raid a drug-house and cocaine are sitting on a table uncovered by anything, and the K-9 starts sniffing it, then we wouldn't know, because scientists never did drug testing on any domestic animals. But most of the time SWAT/Police would NEVER use dogs in a RAID, sometimes just after the raid to chase the suspects.