src/cmd/go/testdata/script/sum_readonly.txt

# Test that go.sum does not get updated when -mod=readonly flag is set
env GO111MODULE=on

go get -d rsc.io/quote
go mod tidy

# go.sum != dirty; -mod=readonly
go list -mod=readonly

# dirty up go.sum by removing it.
rm go.sum

# go.sum == dirty; -mod=readonly
! go list -mod=readonly

stderr 'go: updates to go.sum needed, disabled by -mod=readonly'

-- go.mod --
module m

-- main.go --

package main

import "rsc.io/quote"

func main() {
    println(quote.Hello())
}