In Go 1.24, we introduced the testing/synctest package as an experimental package. This package can significantly simplify writing tests for concurrent, asynchronous code. In Go 1.25, the testing/synctest package has graduated from experiment to general availability. What follows is the blog version of my talk on the testing/synctest package at GopherCon Europe 2025 in Berlin. What is an asynchronous function? A synchronous function is pretty simple. You call it, it does something, and it return...