How can we find a dog to "test drive"?

Many foster agencies will let you let you take a dog for Monday - Friday and then decide. They want to place the dog in a good fit.

Within a breed personalities differ. I would base the decision more on the dog.

I don't know specifically about England, but here in Germany, many pet shelters are looking for volunteers who (regularily) take dogs for a walk. Even if they might not have your specific breed available, interacting with different dogs will teach you a lot about them, and it will allow you to check if you're really that enthusiastic about the daily care a dog needs.

As others have already stated, you'll definitely want to look at organisations that are looking for volunteers for both fostering but also dog walking.

For example, The UK's Blue Cross have a scheme which allows you to walk their dogs for them. I would definitely look at this option even if you think you're already set on your dog breed. I was absolutely set on a specific breed but then fell in love with another one just by meeting it. Don't rule out the option to change your mind. When you walk the dogs, you'll get an opportunity to meet many different ones for a short time (as Guntram Blohm pointed out).

As this RSPCA blog suggests, while you're searching for a new dog, you get the opportunity to help all of the dogs that you regularly walk:

By helping the dogs to become sociable and trusting, this means they stand a much better chance of finding their forever home.

That's got to be a win-win for both parties.

Again, fostering has been mentioned already but specifically for the UK, the Battersea Dogs Home have a great explanation of the process to see if this might be something you'd consider.

https://www.borrowmydoggy.com/ is a website that allows just this - you can get matched with local dog owners to give their dogs walks. It's potentially a simpler starter than fostering. I've not used it personally, but some friends have (as dog owners) and love it.

Other answers are good. One thing you might not have thought of is to go on a walk for an hour every morning and an hour every evening. See how you feel after doing this for a month. Don't allow yourself to miss a session. Can you see yourself sticking to that regime for the next decade rain or shine?

I'd suggest looking for your local dog park. Whether you find a "test" dog or not, it'll give you a chance to see a large variety of breeds and how they will interact with other breeds and humans.

Taking my girlfriend's dog to the park has taught me a lot. For example, she usually isn't very interested in small dogs her size, unless they are some mix of terriers or corgis (also A-Type personalities). Large dogs get harassed into chasing her. She stays away from adult humans. Children are fair game.

Personally I find her hilarious, but some people might not want an A-Type chihuahua-terrier chasing after everything.

Don't get too hung up on specific breeds especially if you are looking to foster. The act of looking after a dog in itself is key to knowing if it's right for you. I tend to think that you need to fit your life around a dog, not the other way around, every animal has its own quirks, issues and anxieties, and you need to work with those.

It sounds like you are new to dogs, so I would recommend fostering/adopting an older dog as a first step, they tend to be easier as they generally speaking, like to just have a good place to rest and it's a good snapshot of life (12-18 years) with a dog in the space of a couple of years, where as a puppy is a ball of excitement and energy for the first few years.

Ease yourself into younger dogs over time. Puppies and rescue dogs alike are both wonderful, but they are a full time commitment like children and so many get returned or dropped off at rescue centres as people jump into something they were just not prepared for. It's great you are doing the research and willing to do what's right to prepare yourself.

If you are dead set on a specific breed, then look to foster dogs with similar personalities and sizes, puppies are also available, but they tend to get snapped up quick.