> AFAIK some types of drug tests can't measure whether you're high on $drug now or if you're taken it before and you're sober now. If you're driving sober but you've taken $drug yesterday, you might be arrested for DWI.

This is true for THC (marijuana) tests that look for metabolites of THC with long half-lives. It takes a very long time for the body to metabolize THC through the different steps and then eliminate those metabolites.

For many of the drugs named in the article their elimination is rapid. For some like fentanyl their concentrations are also low. If someone has an appreciable concentration of fentanyl detectable by a simple test they are very inebriated.