net/http, internal/testenv: find go binary in PATH

Fixes #14901

Change-Id: Ia32e09767374a341c9a36c5d977d47d7d1a82315
Reviewed-on: https://go-review.googlesource.com/20967
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: David Crawshaw <crawshaw@golang.org>

src/go/build/deps_test.go

@@ -168,7 +168,7 @@ var pkgDeps = map[string][]string{
 	"testing":          {"L2", "flag", "fmt", "os", "runtime/debug", "runtime/pprof", "runtime/trace", "time"},
 	"testing/iotest":   {"L2", "log"},
 	"testing/quick":    {"L2", "flag", "fmt", "reflect"},
-	"internal/testenv": {"L2", "os", "testing"},
+	"internal/testenv": {"L2", "OS", "testing"},
 
 	// L4 is defined as L3+fmt+log+time, because in general once
 	// you're using L3 packages, use of fmt, log, or time is not a big deal.

src/internal/testenv/testenv.go

@@ -12,6 +12,7 @@ package testenv
 
 import (
 	"os"
+	"os/exec"
 	"runtime"
 	"strings"
 	"testing"
@@ -62,6 +63,22 @@ func MustHaveGoRun(t *testing.T) {
 	}
 }
 
+// GoToolPath reports the path to the Go tool.
+// If the tool is unavailable GoToolPath calls t.Skip.
+// If the tool should be available and isn't, GoToolPath calls t.Fatal.
+func GoToolPath(t *testing.T) string {
+	MustHaveGoBuild(t)
+	var exeSuffix string
+	if runtime.GOOS == "windows" {
+		exeSuffix = ".exe"
+	}
+	goBin, err := exec.LookPath("go" + exeSuffix)
+	if err != nil {
+		t.Fatal("cannot find go tool: %v", err)
+	}
+	return goBin
+}
+
 // HasExec reports whether the current system can start new processes
 // using os.StartProcess or (more commonly) exec.Command.
 func HasExec() bool {

src/net/http/http_test.go

@@ -10,9 +10,7 @@ import (
 	"bytes"
 	"internal/testenv"
 	"os/exec"
-	"path/filepath"
 	"reflect"
-	"runtime"
 	"testing"
 )
 
@@ -67,16 +65,10 @@ func TestCleanHost(t *testing.T) {
 // This catches accidental dependencies between the HTTP transport and
 // server code.
 func TestCmdGoNoHTTPServer(t *testing.T) {
-	testenv.MustHaveGoBuild(t)
+	goBin := testenv.GoToolPath(t)
-	var exeSuffix string
+	out, err := exec.Command("go", "tool", "nm", goBin).CombinedOutput()
-	if runtime.GOOS == "windows" {
-		exeSuffix = ".exe"
-	}
-
-	goBin := filepath.Join(runtime.GOROOT(), "bin", "go"+exeSuffix)
-	out, err := exec.Command("go", "tool", "nm", goBin).Output()
 	if err != nil {
-		t.Fatalf("go tool nm: %v", err)
+		t.Fatalf("go tool nm: %v: %s", err, out)
 	}
 	wantSym := map[string]bool{
 		// Verify these exist: (sanity checking this test)