$ go mod download
$ go get -u github.com/gin-gonic/gin
$ go run main.go
$ go mod tidy
export PATH=$PATH:$HOME/go/bin
if you cannot find go/src/xxx, then add
-build_flags=--mod=mod
to command
https://dev.to/vuong/golang-in-vscode-show-code-coverage-of-after-saving-test-8g0