// tests to attempt to overwrite the installed standard library.
		// Bail out entirely in this case.
		goHostOS = goEnv("GOHOSTOS")
		os.Setenv("TESTGO_GOHOSTOS", goHostOS)
		goHostArch = goEnv("GOHOSTARCH")
		os.Setenv("TESTGO_GOHOSTARCH", goHostArch)

		cgoEnabled = goEnv("CGO_ENABLED")

		// Duplicate the test executable into the path at testGo, for $PATH.

	// always go to GOROOT/bin anyway.
	os.Setenv("GOBIN", gorootBin)

	// Make the environment more predictable.
	os.Setenv("LANG", "C")
	os.Setenv("LANGUAGE", "en_US.UTF8")
	os.Unsetenv("GO111MODULE")
	os.Setenv("GOENV", "off")
	os.Unsetenv("GOFLAGS")
	os.Setenv("GOWORK", "off")

	workdir = xworkdir()
	if err := os.WriteFile(pathf("%s/go.mod", workdir), []byte("module bootstrap"), 0666); err != nil {

	)
	runcmd := func(args ...string) ([]byte, error) {
		cmd := exec.Command(args[0], args[1:]...)
		var buf bytes.Buffer
		cmd.Stdout = &buf
		cmd.Stderr = &buf
		cmd.Env = append(os.Environ(), "GOENV=off", "GOFLAGS=")
		if runInDir != "" {
			cmd.Dir = runInDir
			// Set PWD to match Dir to speed up os.Getwd in the child process.
			cmd.Env = append(cmd.Env, "PWD="+cmd.Dir)
		} else {