env GO111MODULE=on

go get -d rsc.io/quote@v1.5.1
go mod vendor
env GOPATH=$WORK/empty
env GOPROXY=file:///nonexist

go list -mod=vendor
go list -mod=vendor -m -f '{{.Path}} {{.Version}} {{.Dir}}' all
stdout '^rsc.io/quote v1.5.1 .*vendor[\\/]rsc.io[\\/]quote$'
stdout '^golang.org/x/text v0.0.0.* .*vendor[\\/]golang.org[\\/]x[\\/]text$'

! go list -mod=vendor -m rsc.io/quote@latest
stderr 'module lookup disabled by -mod=vendor'
! go get -mod=vendor -u
stderr 'go get: disabled by -mod=vendor'

-- go.mod --
module x

-- x.go --
package x
import _ "rsc.io/quote"