env GO111MODULE=on

env GOPATH=$WORK${/}invalid-gopath

go list -m
stdout '^example.com$'

go list
stdout '^example.com$'

-- go.mod --
module example.com

go 1.13
-- main.go --
package main

func main() {}

-- $WORK/invalid-gopath
This is a text file, not a directory.