Another possibility is Vitoria-Gasteiz. There's an aire in the centre, in a very large car park, where we have stayed overnight on our way to Bilbao. There's a Covid Test Centre about 45 mins walk away. They say the turn around time is 24-48 hours. The Eurofins site, which has this on its list of centres, says they have an app which will give you the test result. So if you're boarding on Friday for example, get tested on Tuesday and go and do your thing and get your result on the app.
You can also overnight at the port, according to BF.
