I can't reproduce it in windows 10.

C:\Users\rajender\go-contrib\go\src>go test -short -run="Cancel|Race" -count=100 os/exec
ok os/exec 7.981s

C:\Users\rajender\go-contrib\go\src>go version
go version devel +9d5f8eaa8a Fri Dec 15 02:48:35 2017 +0000 windows/amd64

C:\Users\rajender\go-contrib\go\src>go env
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\rajender\AppData\Local\go-build set GOEXE=.exe set GOHOSTARCH=amd64 set GOHOSTOS=windows set GOOS=windows
set GOPATH=C:\Users\rajender\go
set GORACE=
set GOROOT=C:\Users\rajender\go-contrib\go
set GOTMPDIR=
set GOTOOLDIR=C:\Users\rajender\go-contrib\go\pkg\tool\windows_amd64
set GCCGO=gccgo
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
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\rajender\AppData\Local\Temp\go-build924340210=/tmp/go-build -gno-record-gcc-switches

C:\Users\rajender\go-contrib\go\src>

I believe this error means that cmd/go has found some packages in the cache. It has told vet that those packages can be found in the cache. When vet goes to open them, it gets an error.

Looking at the file name, it's weird that it's a relative path. The relevant code is in cmd/go/internal/cache/default.go. On Windows, if GOCACHE is not set in the environment, it uses a subdirectory go-build of whatever is returned by os.Getenv("LocalAppData"). I imagine that in the failing case that environment variable was not set.

Change https://golang.org/cl/85996 mentions this issue: cmd/go: on Windows, disable cache if LocalAppData is not set