if zipErr != nil && errors.Is(zipErr, fs.ErrNotExist) &&
			dirErr != nil && errors.Is(dirErr, fs.ErrNotExist) {
			// Nothing downloaded yet. Nothing to verify.
			return nil
		}
		errs = append(errs, fmt.Errorf("%s %s: missing ziphash: %v", mod.Path, mod.Version, err))
		return errs
	}
	h := string(bytes.TrimSpace(data))

	if zipErr != nil && errors.Is(zipErr, fs.ErrNotExist) {
		// ok
	} else {

// report that a file or directory does not exist. It is satisfied by
// [ErrNotExist] as well as some syscall errors.
//
// This function predates [errors.Is]. It only supports errors returned by
// the os package. New code should use errors.Is(err, fs.ErrNotExist).
func IsNotExist(err error) bool {
	return underlyingErrorIs(err, ErrNotExist)
}

// IsPermission returns a boolean indicating whether the error is known to

	ErrNotExist   = errNotExist()   // "file does not exist"
	ErrClosed     = errClosed()     // "file already closed"
)

func errInvalid() error    { return oserror.ErrInvalid }
func errPermission() error { return oserror.ErrPermission }
func errExist() error      { return oserror.ErrExist }
func errNotExist() error   { return oserror.ErrNotExist }

	QWORD                      = 11
)

var (
	// ErrShortBuffer is returned when the buffer was too short for the operation.
	ErrShortBuffer = syscall.ERROR_MORE_DATA

	// ErrNotExist is returned when a registry key or value does not exist.
	ErrNotExist = syscall.ERROR_FILE_NOT_FOUND

	// ErrUnexpectedType is returned by Get*Value when the value's type was unexpected.
	ErrUnexpectedType = errors.New("unexpected key value type")
)

	// Any error returned aborts the dial and is returned unwrapped.
	StartDial func(network, address string) error

	Question func(dnsmessage.Header, dnsmessage.Question)

	// err may be ErrNotExist or ErrRefused; others map to SERVFAIL (RCode2).
	// A nil error means success.
	HandleA    func(w AWriter, name string) error
	HandleAAAA func(w AAAAWriter, name string) error

	}

	// We try to report the most helpful error to the user. "direct" and "noproxy"
	// errors are best, followed by proxy errors other than ErrNotExist, followed
	// by ErrNotExist.
	//
	// Note that errProxyOff, errNoproxy, and errUseProxy are equivalent to
	// ErrNotExist. errUseProxy should only be returned if "noproxy" is the only
	// proxy. errNoproxy should never be returned, since there should always be a

// license that can be found in the LICENSE file.

package fs_test

import (
	"errors"
	. "io/fs"
	"testing"
)

type subOnly struct{ SubFS }

func (subOnly) Open(name string) (File, error) { return nil, ErrNotExist }

func TestSub(t *testing.T) {
	check := func(desc string, sub FS, err error) {
		t.Helper()
		if err != nil {
			t.Errorf("Sub(sub): %v", err)
			return
		}
		data, err := ReadFile(sub, "goodbye.txt")

		Mode:    0456,
		ModTime: time.Now(),
		Sys:     &sysValue,
	},
}

var sysValue int

type readFileOnly struct{ ReadFileFS }

func (readFileOnly) Open(name string) (File, error) { return nil, ErrNotExist }

type openOnly struct{ FS }

func TestReadFile(t *testing.T) {
	// Test that ReadFile uses the method when present.
	data, err := ReadFile(readFileOnly{testFsys}, "hello.txt")

}

// represents a dnsConfig returned by parsing a nonexistent resolv.conf
var defaultResolvConf = &dnsConfig{
	servers:  defaultNS,
	ndots:    1,
	timeout:  5,
	attempts: 2,
	err:      fs.ErrNotExist,
}

func TestConfHostLookupOrder(t *testing.T) {
	// These tests are written for a system with cgo available,
	// without using the netgo tag.
	if netGoBuildTag {

	if err != path.ErrBadPattern {
		t.Fatalf("Glob returned err=%v, want %v", err, path.ErrBadPattern)
	}
}

type globOnly struct{ GlobFS }

func (globOnly) Open(name string) (File, error) { return nil, ErrNotExist }

func TestGlobMethod(t *testing.T) {
	check := func(desc string, names []string, err error) {
		t.Helper()
		if err != nil || len(names) != 1 || names[0] != "hello.txt" {