…how to lock a piece of code so that it's guaranteed to only run once at a time. If it's running and another thread (or Goroutine in my case) reaches the same piece of code, it will wait for the first process to finish before continuing its execution.

I'm using it to lock an entire function, but apparently it works for any section of code.

Running tests with coverage on the Goland IDE is really easy, you just write the test and it gives you a "play icon" button to the left of each function, and after it runs you get the coverage report in a separate window and within the source code as well, telling you exactly which lines are covered.