Because there is no CoVid 19 test – the test utilized today is the same test utilized in 2003 for SARS-CoV which embraces ALL coronaviruses.
Here is what WHO stated about SARS-CoV testing in 2003:
PCR TEST: Recommendations for laboratories testing for SARS-coronavirus, are very specific and mean that there is genetic material (RNA) of the SARS-CoV in the sample. This does not mean that there is live virus present, or that it is present in a quantity large enough to infect another person. The virus and its genetic material may be present for a brief period only, depending on the type of specimen tested.
ANTIBODY TEST: Positive antibody test results indicate a previous infection with SARS-CoV. Seroconversion from negative to positive or a four-fold rise in antibody titre from acute to convalescent serum indicates recent infection.