Go's tooling is second to none; it's one of the things I like best about it. The sheer number of debugging, benchmarking, live and static analysis tools is enterprise-level.
I will say, while having unit testing as a first-class supported function is fantastic, the test package is a big anemic. I had been using Ruby a lot when I first got into Go, and it was almost harder to write Ruby without doing test-driven development; it was so fantastically easy, it changed my entire vie perspective on unit tests. Go is... harder. There are no assertions built into the test package, mocking is a PITA, and all of those great Go language safety features make writing tests harder. Yes, there are a lot of this party tools to address these things, but honestly I wish testing
had been a bit more built-out. Many of the defacto standard testing practices still dominant today were already well established by the time Go was released; there really was little reason not to provide more tools to make writing tests easier, and thereby encourage test-driven development.
But, really, it's a fairly minor grievance, and far too late to address.