I was actually lucky that my one contribution made it into HA because it was done essentially blind: I had no way to compile my code changes, much less verify them. Thankfully it was small enough that careful inspection was sufficient. But as a SW engineer, that is not how I like to work.
How do I create a HA test instance and populate it with the appropriate git repos (and branches thereof) I can modify and poke at to figure out what is going wrong and hopefully fix it, then run regression tests and eventually submit?
I went through the documentation and could not find a “How to Dev” write-up.