Depends on what you're being tested for. If its for a job then they test for illegal substances. They have to run different panels for other drugs such as steroids even and those get to be expensive so even police (2 of my neighbors are cops) don't test for those. Also, if you're taking legal supplements then you have nothing to worry about anyways because you're legally doing nothing wrong.
Now... if you're an athlete like me and subject to random drug testing thats an different matter entirely. They will test for performance enhancing substances and many legal over the counter items are banned. This type of test is only done for athletes at certain levels and if you're being tested for those you get this all explained to you so my guess is this is not the case for you. Any substances on the World Anti Doping Agency banned substances list are prohibited as per their guidelines and your country may have even stricter guidelines as well. Many professional sports don't even adhere to the WADA prohibited list as they are free to make their own exceptions as they see fit (NFL, NBA, NHL, etc) such as allowing cold and allergy medicines.