A PCR will generally have around a 99% sensitivity and a 95% specificity. That depends on things like the nasal swab going all the way to the back in a deeply uncomfortable way and if they only get the front of the nasal cavity (with Covid-19 in particular) it might be just a 95% sensitivity.
Antibody tests will generally have a much lower sensitivity but can detect whether you had the virus in the past.
Comments
A PCR will generally have around a 99% sensitivity and a 95% specificity. That depends on things like the nasal swab going all the way to the back in a deeply uncomfortable way and if they only get the front of the nasal cavity (with Covid-19 in particular) it might be just a 95% sensitivity.
Antibody tests will generally have a much lower sensitivity but can detect whether you had the virus in the past.