env GO111MODULE=on
env sumdb=$GOSUMDB
env proxy=$GOPROXY
env GOPROXY GONOPROXY GOSUMDB GONOSUMDB

# basic fetch (through proxy) works
cp go.mod.orig go.mod
go get -d rsc.io/fortune@v1.0.0 # note: must use test proxy, does not exist in real world
rm $GOPATH/pkg/mod/cache/download/sumdb # rm sumdb cache but NOT package download cache
rm go.sum

# can fetch by explicit URL
cp go.mod.orig go.mod
env GOSUMDB=$sumdb' '$proxy/sumdb-direct
go get -d rsc.io/fortune@v1.0.0
rm $GOPATH/pkg/mod/cache/download/sumdb
rm go.sum

# direct access fails (because localhost.localdev does not exist)
# The text of the error message is hard to predict because some DNS servers
# will resolve unknown domains like localhost.localdev to a real IP
# to serve ads.
cp go.mod.orig go.mod
env GOSUMDB=$sumdb
env GOPROXY=direct
! go get -d rsc.io/fortune@v1.0.0
stderr 'verifying.*localhost.localdev'
rm $GOPATH/pkg/mod/cache/download/sumdb
rm go.sum

# proxy 404 falls back to direct access (which fails)
cp go.mod.orig go.mod
env GOSUMDB=$sumdb
env GOPROXY=$proxy/sumdb-404
! go get -d rsc.io/fortune@v1.0.0
stderr 'verifying.*localhost.localdev'
rm $GOPATH/pkg/mod/cache/download/sumdb
rm go.sum

# proxy non-200/404/410 stops direct access
cp go.mod.orig go.mod
env GOSUMDB=$sumdb
env GOPROXY=$proxy/sumdb-503
! go get -d rsc.io/fortune@v1.0.0
stderr '503 Service Unavailable'
rm $GOPATH/pkg/mod/cache/download/sumdb
rm go.sum

-- go.mod.orig --
module m