A respirator fit test can be described as a type of testing protocol that is conducted with the intent to certify that a respirator fits someone's face in a way that is both comfortable and also effectively provides that person with the protection that is expected.

Respirator Fit Testing Methods: Qualitative & Quantitative
The most important distinction when looking at qualitative vs. quantitative respirator fit testing is that qualitative testing relies on the wearer's senses to notice leaks. On the other hand, with quantitative testing, leakage is measured with instruments and does not rely on the wearer to provide information.