A negative coronavirus test doesn't always mean you are not infected/ WaPo

Various interviewees estimated the that the coronavirus tests they are familiar with are 75%, 85% or 100% accurate:

Demetre Daskalakis, deputy commissioner for the division of disease control of the New York City Department of Health and Mental Hygiene, said he recently told a patient with mild symptoms who sought a test and received a negative result to act like he had it.
“The pretest probability if you have fever or cough in a pandemic — if you have a fever, cough and shortness of breath, it’s covid-19. Even if the test is negative,” Daskalakis said.