Playtests are the lifeblood of board game design. A game might go through a hundred revisions, and will need a playtest each time.
If you don't have a reliable source
of playtests, you can't really design board games. You can also only
design at the speed of your access to playtests.
Playtesting against yourself is unsatisfying, and it's not a genuine game experience. Also, other people's feedback is essential.
You need playtesters, but you also need a variety of playtesters. These different groups will all have different aptitudes and preferences.
If you have a partner or very good friend, who's happy to consistently playtest more than once a week, you have no problems.
I run a games group regularly, at my house. Friends are happy to playtest, but not too regularly.
Friends and family are also useful for very early playtests. They'll be much more tolerant of things going wrong.
I joined a board games club, mainly as a source of testers for my games. I enjoy playing board games there, but people come to play published games, and I get only the occasional playtest in. This is not an ideal place to go for playtesting.
I've seen these, and attended meetups. These might be a great place to get very hands-on feedback, if you're new. More likely, they're a huge time-sink, as you spend all afternoon playing other people's big games.
A group is still not a terrible choice.
I'm not a huge fan of online communities, for board game design. Just like in real life groups, everyone is looking to have their own game tested. People with long multiplayer games will soak up huge amounts of playtest time, and not be able to reciprocate. Many people will be late in the design of their deeply flawed first game, and there won't be much you can do to help.
Discord is a program that allows you to form groups, and chat with people. I got onto Discord in about 2017, and there were a few other board game designers on there. This is the place to be. Go and search for board game design Discord servers on Google. Discord runs in your browser, so there's nothing you're required to download.
It's good to get to acquire a game design buddy or two. You want someone with the same level of seriousness as yourself.
This will be a reciprocal arrangement, where you test each other's games. It's very helpful to have someone who knows your game well, and can discuss changes with you. They'll also be crucial when you're early in design, and the game isn't fun yet, and after big changes, when things often break. You can work under the expectation that the game won't be good, without any pressure.
Helping someone else with their game will teach you things, as well. It's like a second game you're working on, but you don't have to do any work.
Whenever I play another designer's game, I try to solve the game's problems as though it were my own game.
A buddy is also a very good source of motivation. Even when you're busy or unmotivated, you keep helping with their game, and it keeps you connected to game design.
Board game design communities are overwhelmingly composed of level-headed and intelligent men in their 30's.
Playing other people's games, even unreciprocated, is still very helpful. Analysing what's wrong with other games will help you develop your own methodology, which is what you'll need, in order to excel.
Once you have your online playtesters, you'll need Tabletop Simulator (TTS). That's what almost everyone uses for playtesting online. It costs $20, and simply provides a 3D space containing a table. You can import cards and other bits into the space, and play all kinds of games in there.
I use Discord, to chat with people, and we playtest each other's games. Feel free to get on a Discord server, and ask people more about Tabletop Simulator.
I haven't done real-life testing since about 2017.
You're probably going to need to teach your playtesters. This is what I've found. The more they understand game design, the better. Help them understand what you want from them.
Being a player and a playtester are entirely different things. Players like to exploit and optimise the game. Designers are creating the padded room in which such craziness can safely occur. When asked to submit cards or ideas, newer playtesters will typically submit wild and zany designs, because they're suddenly free of all restriction.
Playtesters are too concerned with balance and power. They just
assume that fun is ubiquitous in games, and it can be hard for them to
stop thinking about power, and start thinking about fun. They're players, and you need to make designers out of them.
Listen to the playtesters' problems. Generally, ignore their solutions, and fix their problems your own way. Their experience is never wrong, but their suggestions usually are.
Thank your playtesters. Unless the arrangement is reciprocal, they're doing you a huge favour. Don't waste their time. End the playtest before they get tired of it. They'll appreciate that. Just test long enough to get a feel for the game. Don't make them play a whole game of an early prototype.
As with any group, playtesters will drift away, and you'll need a constant stream of new recruits.
If you're a published designer, you have access to the ultimate source of playtesters: your game's fan base.
I needed playtesters, so I posted a request on the Radlands forums. I ended up getting more playtesters than I'll ever need.
Fans will be excited to be given the honour of helping you, the great designer of their favourite game, and you don't have to playtest their game.