There are a variety of tests available but it is important to consider what they test for.
Antibody testing offered by some companies, will confirm whether or not the individual has developed antibodies for the virus, thus suggesting that they have already had the virus. However, the World Health Organisation has advised that as yet there is no evidence to support that individuals who have developed antibodies are then immune, and as such they could still catch it again.
Alternatively, NHS tests undertaken at hospitals or official test centres, test for the presence of the virus . If you test positive for the virus, you are required to self-isolate to prevent spreading to others.
As such it is likely that an individual could test negative for antibodies and positive for the virus, as the antibodies have not yet been developed in response to the virus.
Official advice is that if you have symptoms you should self-isolate for 7 days (and the rest of the household for 14 days). However, key workers are now able to be tested by NHS for the presence of the virus, so that you know if you do indeed have the virus and need to isolate.