Sometimes people will ask me if I can join them to assess a dog or a puppy before they adopt. I am happy to do that but it's important to realize that "temperament test" is a bit of a misnomer. There is no 15 minute test that tells us everything we need to know about a puppy or a dog from now through forever. They are affected by genetics, environment, and training methods. It's more accurate to call these evaluations "behavior assessments" because they give us a snapshot of the dog's behavior on a given day at a given time under certain circumstances.
That's why I think dogs are like restaurants. Think about a restaurant you've been to recently. Maybe you had never been and someone recommended it, giving it rave reviews but then you arrived and it was just so-so. Maybe a chef was having a bad day, maybe the waiter spilled your soup, who knows. On any given day a restaurant can be wonderful or terrible, depending on lots of different factors. We can only get a picture of the consistent quality of the restaurant with multiple visits on multiple days. We also judge restaurants based on our own experiences and biases and people describing dogs and puppies we are interested in adopting are only human - they also may let their opinions of a dog be influenced by their own preferences.
What does that mean for adopting a dog? Your best bet is to meet the dog's parents if possible, see the dog more than once, handle the dog (carefully), see what happens if you ignore the dog and if you get the dog riled up. Try to see the dog in multiple environments, if you can, and consider what kind of environment the dog will live in later, too. If you live in the city and are looking at a dog raised in a quiet, rural environment, plopping that dog into a noisy city may cause the dog to act differently. Dogs who are assessed in shelters are often being examined while pretty stressed out and that may influence their assessments.
If you are working with a shelter or rescue, ask to see behavior assessment worksheets. There are multiple assessment frameworks available to professionals like SAFER, Canine-ality, Assess a pet, and more. They are designed to be somewhat impartial and help determine whether a dog is a good fit for a family's lifestyle. If a dog is in foster and there is no assessment, at least ask what the home is like, how active it is, what the routine is like, whether the dog has met any dogs /cats/ kids, etc... and how it went, whether the dog has ever seem scared or angry, whether the dog has growled or snapped or bitten, etc...
Your best bet is to ask a reputable trainer if they recommend adopting from certain shelters, rescues, or breeders. They often have seen many dogs coming out of these places and have a better feel for how well dogs and puppies are being matched with families.