我有这个：
cd /tmp/proj
echo '(content)' > go.mod
go mod download # create modules cach --> could be weeks or months old!!
cd $GOPATH/src/acme/proj
go install -v # should be sped up since `go mod download` was run prior?
how can I confirm that it's using the cache created by go mod download? The go install command does not seem to run significantly faster :/
