Wikipedia: Pill Testing

A test is done by taking a small scraping from a pill and placing it in the reagent testing liquid. The liquid will change colour when reacting with different chemicals to indicate the presence of certain substances. Testing with a reagent kit does not indicate the pill is safe. While the testing process does show some particular substances are present, it may not show a harmful substance unaccounted for by the testing process. Testing kits are distributed on a not-for-profit basis by Dancesafe and commercially.