cmd/go: dependency only used in test code can not be found

[cloudfstrife]

What version of Go are you using (go version)?

$ go version
go version go1.12.5 windows/amd64

Does this issue reproduce with the latest release?

I use the latest version

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\Cloud.F.Strife\AppData\Local\go-build
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows
set GOPATH=E:\go\env
set GOPROXY=
set GORACE=
set GOROOT=D:\go
set GOTMPDIR=
set GOTOOLDIR=D:\go\pkg\tool\windows_amd64
set GCCGO=gccgo
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=E:\space\testing\go.mod
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\CLOUDF~1.STR\AppData\Local\Temp\go-build307206806=/tmp/go-build -gno-record-gcc-switches

What did you do?

testing code is this

.
|-- fibonacci
|   |-- fibonacci.go
|   `-- fibonacci_test.go
|-- go.mod
`-- go.sum

go.mod file

module app/testing

go 1.12

require github.com/google/go-cmp v0.3.0 // indirect

fibonacci.go do not import any module

fibonacci/fibonacci_test.go import github.com/google/go-cmp

package fibonacci

import (
        "fmt"
        "testing"

        "github.com/google/go-cmp"
)

when i run go test -v app/testing/fibonacci , i got an error:

$ go test -v app/testing/fibonacci
# app/testing/fibonacci
fibonacci\fibonacci_test.go:7:2: unknown import path "github.com/google/go-cmp": cannot find module providing package github.com/google/go-cmp
FAIL    app/testing/fibonacci [setup failed]

when i run go mod tidy , the go-cmp dependency in go.mod disappeared

What did you expect to see?

did i use go module in wrong way ? what can i do to resolve this problem?

What did you see instead?

[andybons]

@jayconrod @bcmills

[jayconrod]

I think you meant to import github.com/google/go-cmp/cmp? There is no package with the path github.com/google/go-cmp, though that is the correct module path.

The error message could be a bit clearer. #30723 is the main issue for that.

[cloudfstrife]

thanks a lot