How to measure code coverage in Go?

Hello, colleagues! I've just started learning Go, and I'm having a problem with measuring code coverage. I'm writing a small REST API using net/http, and I want to make sure my tests cover all the main scenarios. Here's an example of my code: ```go package main import ( "net/http" "testing" ) func handler(w http.ResponseWriter, r *http.Request) { w.Write([]byte("Hello, World!")) } func TestHandler(t *testing.T) { req, _ := http.NewRequest("GET", "/", nil) rr := httptest.NewRecorder() handler(rr, req) if rr.Code != http.StatusOK { t.Errorf("expected 200, got %d", rr.Code) } } ``` I run tests via `go test`, but how do I find out what percentage of code is covered by tests? The documentation mentions the `-cover` flag, but I don't understand how to use it.