The unit is currently at Aston Street car park, in the town.
Health bosses say it is open daily from 9am to 3pm until August 8.
"Booking is essential and can be done online at gov.uk/get-coronavirus-test," a spokesman said.
If you have any of the three main symptoms, even if it's only mild, you should get a PCR test as soon as possible:
They are a high temperature, a new, continuous cough or the loss of sense of smell or taste or it has changed.
Home test kits can be picked up at a number of sites.