Looking back on the 2010's, how was it?

[The Adventurer's Almanac]

I got into good testing practices - my homebrew became significantly more rigorously tested as a result.

Where exactly might one find these practices?

[Koumei]

I'm surprised you haven't brought up the new Space Marine supplements where GW took...a fairly balanced meta and kicked it in the nuts.

I just don't care about 40K enough to be bothered by the new Space Marine supplements. The new system is enough of a train wreck that it doesn't really matter what they do with it.

[Whiysper]

I got into good testing practices - my homebrew became significantly more rigorously tested as a result.

Where exactly might one find these practices?

I can't give you a direct link that's really applicable, but basically adopting the idea of Unit Testing - that you should be able to run the same test, repeatably, on a given section of the rules, and that every time you change anything that interacts with them, you re-run those tests.

It's slowed me down, because that does actually mean things like running whole games and finding opportunities to test out, say, item damage rules, or infection rules, or whatever.
Combat is an obvious and easy place to start - you've presumably worked out how a fight between an X and a Y should go. So every time you change anything that either X or Y uses, or terrain, or visibility, or... you re-run the fight a few times, check your numbers, and ensure that you haven't just thrown a wheel before you let those rules anywhere near the playtesters/players.

Hope that helps .