DH and I haven't always agreed on all things gifted but through time and a lot of talk (and a bottle or two of wine haha) we've figured out ways to proceed that we both agreed on. Much of this stemmed from our own experiences as (likely) gifted kids ourselves. We had very different experiences which led to very different hang ups and views. I'll also add that as our kids have grown up and experienced things for themselves we've often had to adjust.
I see two potential concerns and it might be good to discuss them separately
1. the testing itself - the waste of time comment might suggest that he doesn't trust/believe the results? Perhaps he went through testing and didn't feel that the results matched him (either an over or under-estimation)? maybe he views testing as having too narrow of a focus? Maybe he views IQ as being not important in general?
2. what might happen as a result of the testing which also breaks down into a couple things -
being labeled - perhaps he's worried about how your DS will be treated by teachers/admins/peers, perhaps he's worried that DS will coast or become arrogant about the label, perhaps he's worried that the label will become something to live up to?
shipped off to another school - perhaps he's worried about a long commute, missed opportunities of neighbourhood classmates, explaining to others who want to know why they aren't at the local school, no longer walking to school, moving schools too often, etc
I think in order to move forward you need to dig more into WHY he is against it. Depending on the answers there might be ways around it or you might have to agree to disagree (at least for now). DH and I have talked for hours and dug into a lot of our own experiences. We both had very valid reasons for the beliefs and views that we had/have. Talking them through and seeing it from the other person's view was really useful and in the end, I think resulted in better decisions. As time went on we've also both shifted our views on some things based on what our children were experiencing.
I'll also add that one potential compromise might be to test privately (although admittedly then $$$ is a factor). We tested privately which meant that the school only knew what we wanted to share with them (might work if the label part turns out to be a key issue). In our case, we shared the whole report but if the results had not explained things or matched the child or opened doors that we felt were useful we could have kept the results to ourselves. I'll also add that we held off shipping our kids off to another school for a variety of reasons but in the end, that's what we ended up deciding to do. DH was hesitant but after we exhausting all other options he agreed to give it a try. A few months later he had no hesitation when it came to child #2. I'll also admit that there were upsides to the kids experiencing exhausting the other options.
