cmd/go: fix go test using package main_test

A package main binary (that is, a command) being installed
does not mean we can skip the build of the package archive
during a test.

Fixes #3417.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/13462046

src/cmd/go/test.bash

@@ -138,6 +138,27 @@ elif ! test -x testdata/bin/go-cmd-test; then
 	ok=false
 fi
 
+TEST package main_test imports archive not binary
+export GOBIN=$(pwd)/testdata/bin
+mkdir -p $GOBIN
+export GOPATH=$(pwd)/testdata
+touch ./testdata/src/main_test/m.go
+if ! ./testgo test main_test; then
+	echo "go test main_test failed without install"
+	ok=false
+elif ! ./testgo install main_test; then
+	echo "go test main_test failed"
+	ok=false
+elif [ "$(./testgo list -f '{{.Stale}}' main_test)" != false ]; then
+	echo "after go install, main listed as stale"
+	ok=false
+elif ! ./testgo test main_test; then
+	echo "go test main_test failed after install"
+	ok=false
+fi
+rm -rf $GOBIN
+unset GOBIN
+
 # And with $GOBIN set, binaries get installed to $GOBIN.
 TEST install into GOBIN
 if ! GOBIN=$(pwd)/testdata/bin1 GOPATH=$(pwd)/testdata ./testgo install go-cmd-test; then

src/cmd/go/test.go

@@ -590,7 +590,7 @@ func (b *builder) test(p *Package) (buildAction, runAction, printAction *action,
 	localCover := testCover && testCoverPaths == nil
 
 	// Test package.
-	if len(p.TestGoFiles) > 0 || localCover {
+	if len(p.TestGoFiles) > 0 || localCover || p.Name == "main" {
 		ptest = new(Package)
 		*ptest = *p
 		ptest.GoFiles = nil

src/cmd/go/testdata/src/main_test/m.go

+package main
+
+func F()    {}
+func main() {}

src/cmd/go/testdata/src/main_test/m_test.go

+package main_test
+
+import (
+	. "main_test"
+	"testing"
+)
+
+func Test1(t *testing.T) {
+	F()
+}