defer chtmpdir(t)()
	const f = "append.txt"
	s := writeFile(t, f, O_CREATE|O_TRUNC|O_RDWR, "new")
	if s != "new" {
		t.Fatalf("writeFile: have %q want %q", s, "new")
	}
	s = writeFile(t, f, O_APPEND|O_RDWR, "|append")
	if s != "new|append" {
		t.Fatalf("writeFile: have %q want %q", s, "new|append")
	}
	s = writeFile(t, f, O_CREATE|O_APPEND|O_RDWR, "|append")
	if s != "new|append|append" {

	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 {
		fatalf("cannot write stub go.mod: %s", err)
	}
	xatexit(rmworkdir)

	tooldir = pathf("%s/pkg/tool/%s_%s", goroot, gohostos, gohostarch)

{
  .debug_gdb_scripts BLOCK(__section_alignment__) (NOLOAD) :
  {
    *(.debug_gdb_scripts)
  }
}
INSERT AFTER .debug_types;
`
	err := os.WriteFile(path, []byte(src), 0666)
	if err != nil {
		Errorf(nil, "WriteFile %s failed: %v", name, err)
	}
	return path
}

type machoUpdateFunc func(ctxt *Link, exef *os.File, exem *macho.File, outexe string) error

func testFileServerImplicitLeadingSlash(t *testing.T, mode testMode) {
	tempDir := t.TempDir()
	if err := os.WriteFile(filepath.Join(tempDir, "foo.txt"), []byte("Hello world"), 0644); err != nil {
		t.Fatalf("WriteFile: %v", err)
	}
	ts := newClientServerTest(t, mode, StripPrefix("/bar/", FileServer(Dir(tempDir)))).ts
	get := func(suffix string) string {

	uuid, _ := uuid2.NewRandom()
	for _, drive := range fsDirs {
		dir := path.Join(drive, bucket, object, uuid.String())
		err = os.MkdirAll(dir, os.ModePerm)
		if err != nil {
			t.Fatal(err)
		}
		err = os.WriteFile(pathJoin(dir, "part.1"), []byte("some data"), os.ModePerm)
		if err != nil {
			t.Fatal(err)
		}
	}

	// This should remove all the unreferenced parts.

		if err != nil {
			t.Fatal(err)
		}
		old := data
		data = append(data, fmt.Sprintf("var DummyUnusedVar%d bool\n", idx)...)
		if err := os.WriteFile(name, append(data, '\n'), 0666); err != nil {
			t.Fatal(err)
		}
		tg.sleep()
		return func() {
			if err := os.WriteFile(name, old, 0666); err != nil {
				t.Fatal(err)
			}
		}
	}

	// Every main package depends on the "runtime".

// WriteWorkFile cleans and writes out the go.work file to the given path.
func WriteWorkFile(path string, wf *modfile.WorkFile) error {
	wf.SortBlocks()
	wf.Cleanup()
	out := modfile.Format(wf.Syntax)

	return os.WriteFile(path, out, 0666)
}

// UpdateWorkGoVersion updates the go line in wf to be at least goVers,
// reporting whether it changed the file.
func UpdateWorkGoVersion(wf *modfile.WorkFile, goVers string) (changed bool) {

		// See runtime/unsafepoint_test.go.
		pmain.Internal.OmitDebug = false
	}

	if !cfg.BuildN {
		// writeTestmain writes _testmain.go,
		// using the test description gathered in t.
		if err := os.WriteFile(testDir+"_testmain.go", *pmain.Internal.TestmainGo, 0666); err != nil {
			return nil, nil, nil, err
		}
	}

	// Set compile objdir to testDir we've already created,