Many of the replies on this thread show that the tests should be charged for. So many people don't think through what they are going to do with the information the test supplies when they get it. No point in testing if you weren't going to do something that might pass on Covid if you were positive, anyway. Some people seem to think that testing will magically prevent them from catching Covid.
So, about to go and see someone vulnerable or to go to place where there are a lot of people indoors for a longish period (eg church, theatre, long train journey)? Do a test shortly before you leave home. Just one. Use the information that you are probably infectious. Don't go if positive.
Having an operation on, say, Friday? Do a test on the Thursday before to warn the hospital that you are positive. A negative test on Monday, Tuesday or Wednesday provides no useful information at all about whether or not you will be infectious on Friday. And it's unlikely that warning the hospital so early will be much help as, if you are cancelled, they will have no idea who might be clear to take your place until Thursday.
Visiting a vulnerable person? Test yourself just before you go. If positive, don't go. If you live with other people and are concerned about catching Covid from them you need to isolate from them before they show positive on a test, so their test will tell you that you could well be infectious even if negative, so you should cancel the visit. If you go anyway because you are negative, the other people's tests were wasted.
Testing more than once a day? If you are going to be in contact with a vulnerable person more than once, possibly a good idea, so you can be aware that you are positive ASAP and cancel future contacts, and warn the last person you saw before the test that they are at risk. Testing when you get up in the morning and again when you go to bed? Will you alter your getting-into-bed behaviour to minimise risk to another? If not, bedtime test is wasted.
Daily testing because you are a contact? If you, and everyone you live with are not going out of the house for several days, why waste a test? If you're staying in anyway, how can you change your 'spreading' behaviour if you know you're positive? Test before you, or someone you live with, plans to go out and you know that a) you should stay in and b) the other person should test and be cautious.