Adding upstream version 1.22.1.upstream/1.22.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 697 insertions, 0 deletions

diff --git a/src/io/io_test.go b/src/io/io_test.go
new file mode 100644
index 0000000..9491ffa
--- /dev/null
+++ b/src/io/io_test.go
@@ -0,0 +1,697 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package io_test
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	. "io"
+	"os"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"testing"
+)
+
+// A version of bytes.Buffer without ReadFrom and WriteTo
+type Buffer struct {
+	bytes.Buffer
+	ReaderFrom // conflicts with and hides bytes.Buffer's ReaderFrom.
+	WriterTo   // conflicts with and hides bytes.Buffer's WriterTo.
+}
+
+// Simple tests, primarily to verify the ReadFrom and WriteTo callouts inside Copy, CopyBuffer and CopyN.
+
+func TestCopy(t *testing.T) {
+	rb := new(Buffer)
+	wb := new(Buffer)
+	rb.WriteString("hello, world.")
+	Copy(wb, rb)
+	if wb.String() != "hello, world." {
+		t.Errorf("Copy did not work properly")
+	}
+}
+
+func TestCopyNegative(t *testing.T) {
+	rb := new(Buffer)
+	wb := new(Buffer)
+	rb.WriteString("hello")
+	Copy(wb, &LimitedReader{R: rb, N: -1})
+	if wb.String() != "" {
+		t.Errorf("Copy on LimitedReader with N<0 copied data")
+	}
+
+	CopyN(wb, rb, -1)
+	if wb.String() != "" {
+		t.Errorf("CopyN with N<0 copied data")
+	}
+}
+
+func TestCopyBuffer(t *testing.T) {
+	rb := new(Buffer)
+	wb := new(Buffer)
+	rb.WriteString("hello, world.")
+	CopyBuffer(wb, rb, make([]byte, 1)) // Tiny buffer to keep it honest.
+	if wb.String() != "hello, world." {
+		t.Errorf("CopyBuffer did not work properly")
+	}
+}
+
+func TestCopyBufferNil(t *testing.T) {
+	rb := new(Buffer)
+	wb := new(Buffer)
+	rb.WriteString("hello, world.")
+	CopyBuffer(wb, rb, nil) // Should allocate a buffer.
+	if wb.String() != "hello, world." {
+		t.Errorf("CopyBuffer did not work properly")
+	}
+}
+
+func TestCopyReadFrom(t *testing.T) {
+	rb := new(Buffer)
+	wb := new(bytes.Buffer) // implements ReadFrom.
+	rb.WriteString("hello, world.")
+	Copy(wb, rb)
+	if wb.String() != "hello, world." {
+		t.Errorf("Copy did not work properly")
+	}
+}
+
+func TestCopyWriteTo(t *testing.T) {
+	rb := new(bytes.Buffer) // implements WriteTo.
+	wb := new(Buffer)
+	rb.WriteString("hello, world.")
+	Copy(wb, rb)
+	if wb.String() != "hello, world." {
+		t.Errorf("Copy did not work properly")
+	}
+}
+
+// Version of bytes.Buffer that checks whether WriteTo was called or not
+type writeToChecker struct {
+	bytes.Buffer
+	writeToCalled bool
+}
+
+func (wt *writeToChecker) WriteTo(w Writer) (int64, error) {
+	wt.writeToCalled = true
+	return wt.Buffer.WriteTo(w)
+}
+
+// It's preferable to choose WriterTo over ReaderFrom, since a WriterTo can issue one large write,
+// while the ReaderFrom must read until EOF, potentially allocating when running out of buffer.
+// Make sure that we choose WriterTo when both are implemented.
+func TestCopyPriority(t *testing.T) {
+	rb := new(writeToChecker)
+	wb := new(bytes.Buffer)
+	rb.WriteString("hello, world.")
+	Copy(wb, rb)
+	if wb.String() != "hello, world." {
+		t.Errorf("Copy did not work properly")
+	} else if !rb.writeToCalled {
+		t.Errorf("WriteTo was not prioritized over ReadFrom")
+	}
+}
+
+type zeroErrReader struct {
+	err error
+}
+
+func (r zeroErrReader) Read(p []byte) (int, error) {
+	return copy(p, []byte{0}), r.err
+}
+
+type errWriter struct {
+	err error
+}
+
+func (w errWriter) Write([]byte) (int, error) {
+	return 0, w.err
+}
+
+// In case a Read results in an error with non-zero bytes read, and
+// the subsequent Write also results in an error, the error from Write
+// is returned, as it is the one that prevented progressing further.
+func TestCopyReadErrWriteErr(t *testing.T) {
+	er, ew := errors.New("readError"), errors.New("writeError")
+	r, w := zeroErrReader{err: er}, errWriter{err: ew}
+	n, err := Copy(w, r)
+	if n != 0 || err != ew {
+		t.Errorf("Copy(zeroErrReader, errWriter) = %d, %v; want 0, writeError", n, err)
+	}
+}
+
+func TestCopyN(t *testing.T) {
+	rb := new(Buffer)
+	wb := new(Buffer)
+	rb.WriteString("hello, world.")
+	CopyN(wb, rb, 5)
+	if wb.String() != "hello" {
+		t.Errorf("CopyN did not work properly")
+	}
+}
+
+func TestCopyNReadFrom(t *testing.T) {
+	rb := new(Buffer)
+	wb := new(bytes.Buffer) // implements ReadFrom.
+	rb.WriteString("hello")
+	CopyN(wb, rb, 5)
+	if wb.String() != "hello" {
+		t.Errorf("CopyN did not work properly")
+	}
+}
+
+func TestCopyNWriteTo(t *testing.T) {
+	rb := new(bytes.Buffer) // implements WriteTo.
+	wb := new(Buffer)
+	rb.WriteString("hello, world.")
+	CopyN(wb, rb, 5)
+	if wb.String() != "hello" {
+		t.Errorf("CopyN did not work properly")
+	}
+}
+
+func BenchmarkCopyNSmall(b *testing.B) {
+	bs := bytes.Repeat([]byte{0}, 512+1)
+	rd := bytes.NewReader(bs)
+	buf := new(Buffer)
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		CopyN(buf, rd, 512)
+		rd.Reset(bs)
+	}
+}
+
+func BenchmarkCopyNLarge(b *testing.B) {
+	bs := bytes.Repeat([]byte{0}, (32*1024)+1)
+	rd := bytes.NewReader(bs)
+	buf := new(Buffer)
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		CopyN(buf, rd, 32*1024)
+		rd.Reset(bs)
+	}
+}
+
+type noReadFrom struct {
+	w Writer
+}
+
+func (w *noReadFrom) Write(p []byte) (n int, err error) {
+	return w.w.Write(p)
+}
+
+type wantedAndErrReader struct{}
+
+func (wantedAndErrReader) Read(p []byte) (int, error) {
+	return len(p), errors.New("wantedAndErrReader error")
+}
+
+func TestCopyNEOF(t *testing.T) {
+	// Test that EOF behavior is the same regardless of whether
+	// argument to CopyN has ReadFrom.
+
+	b := new(bytes.Buffer)
+
+	n, err := CopyN(&noReadFrom{b}, strings.NewReader("foo"), 3)
+	if n != 3 || err != nil {
+		t.Errorf("CopyN(noReadFrom, foo, 3) = %d, %v; want 3, nil", n, err)
+	}
+
+	n, err = CopyN(&noReadFrom{b}, strings.NewReader("foo"), 4)
+	if n != 3 || err != EOF {
+		t.Errorf("CopyN(noReadFrom, foo, 4) = %d, %v; want 3, EOF", n, err)
+	}
+
+	n, err = CopyN(b, strings.NewReader("foo"), 3) // b has read from
+	if n != 3 || err != nil {
+		t.Errorf("CopyN(bytes.Buffer, foo, 3) = %d, %v; want 3, nil", n, err)
+	}
+
+	n, err = CopyN(b, strings.NewReader("foo"), 4) // b has read from
+	if n != 3 || err != EOF {
+		t.Errorf("CopyN(bytes.Buffer, foo, 4) = %d, %v; want 3, EOF", n, err)
+	}
+
+	n, err = CopyN(b, wantedAndErrReader{}, 5)
+	if n != 5 || err != nil {
+		t.Errorf("CopyN(bytes.Buffer, wantedAndErrReader, 5) = %d, %v; want 5, nil", n, err)
+	}
+
+	n, err = CopyN(&noReadFrom{b}, wantedAndErrReader{}, 5)
+	if n != 5 || err != nil {
+		t.Errorf("CopyN(noReadFrom, wantedAndErrReader, 5) = %d, %v; want 5, nil", n, err)
+	}
+}
+
+func TestReadAtLeast(t *testing.T) {
+	var rb bytes.Buffer
+	testReadAtLeast(t, &rb)
+}
+
+// A version of bytes.Buffer that returns n > 0, err on Read
+// when the input is exhausted.
+type dataAndErrorBuffer struct {
+	err error
+	bytes.Buffer
+}
+
+func (r *dataAndErrorBuffer) Read(p []byte) (n int, err error) {
+	n, err = r.Buffer.Read(p)
+	if n > 0 && r.Buffer.Len() == 0 && err == nil {
+		err = r.err
+	}
+	return
+}
+
+func TestReadAtLeastWithDataAndEOF(t *testing.T) {
+	var rb dataAndErrorBuffer
+	rb.err = EOF
+	testReadAtLeast(t, &rb)
+}
+
+func TestReadAtLeastWithDataAndError(t *testing.T) {
+	var rb dataAndErrorBuffer
+	rb.err = fmt.Errorf("fake error")
+	testReadAtLeast(t, &rb)
+}
+
+func testReadAtLeast(t *testing.T, rb ReadWriter) {
+	rb.Write([]byte("0123"))
+	buf := make([]byte, 2)
+	n, err := ReadAtLeast(rb, buf, 2)
+	if err != nil {
+		t.Error(err)
+	}
+	if n != 2 {
+		t.Errorf("expected to have read 2 bytes, got %v", n)
+	}
+	n, err = ReadAtLeast(rb, buf, 4)
+	if err != ErrShortBuffer {
+		t.Errorf("expected ErrShortBuffer got %v", err)
+	}
+	if n != 0 {
+		t.Errorf("expected to have read 0 bytes, got %v", n)
+	}
+	n, err = ReadAtLeast(rb, buf, 1)
+	if err != nil {
+		t.Error(err)
+	}
+	if n != 2 {
+		t.Errorf("expected to have read 2 bytes, got %v", n)
+	}
+	n, err = ReadAtLeast(rb, buf, 2)
+	if err != EOF {
+		t.Errorf("expected EOF, got %v", err)
+	}
+	if n != 0 {
+		t.Errorf("expected to have read 0 bytes, got %v", n)
+	}
+	rb.Write([]byte("4"))
+	n, err = ReadAtLeast(rb, buf, 2)
+	want := ErrUnexpectedEOF
+	if rb, ok := rb.(*dataAndErrorBuffer); ok && rb.err != EOF {
+		want = rb.err
+	}
+	if err != want {
+		t.Errorf("expected %v, got %v", want, err)
+	}
+	if n != 1 {
+		t.Errorf("expected to have read 1 bytes, got %v", n)
+	}
+}
+
+func TestTeeReader(t *testing.T) {
+	src := []byte("hello, world")
+	dst := make([]byte, len(src))
+	rb := bytes.NewBuffer(src)
+	wb := new(bytes.Buffer)
+	r := TeeReader(rb, wb)
+	if n, err := ReadFull(r, dst); err != nil || n != len(src) {
+		t.Fatalf("ReadFull(r, dst) = %d, %v; want %d, nil", n, err, len(src))
+	}
+	if !bytes.Equal(dst, src) {
+		t.Errorf("bytes read = %q want %q", dst, src)
+	}
+	if !bytes.Equal(wb.Bytes(), src) {
+		t.Errorf("bytes written = %q want %q", wb.Bytes(), src)
+	}
+	if n, err := r.Read(dst); n != 0 || err != EOF {
+		t.Errorf("r.Read at EOF = %d, %v want 0, EOF", n, err)
+	}
+	rb = bytes.NewBuffer(src)
+	pr, pw := Pipe()
+	pr.Close()
+	r = TeeReader(rb, pw)
+	if n, err := ReadFull(r, dst); n != 0 || err != ErrClosedPipe {
+		t.Errorf("closed tee: ReadFull(r, dst) = %d, %v; want 0, EPIPE", n, err)
+	}
+}
+
+func TestSectionReader_ReadAt(t *testing.T) {
+	dat := "a long sample data, 1234567890"
+	tests := []struct {
+		data   string
+		off    int
+		n      int
+		bufLen int
+		at     int
+		exp    string
+		err    error
+	}{
+		{data: "", off: 0, n: 10, bufLen: 2, at: 0, exp: "", err: EOF},
+		{data: dat, off: 0, n: len(dat), bufLen: 0, at: 0, exp: "", err: nil},
+		{data: dat, off: len(dat), n: 1, bufLen: 1, at: 0, exp: "", err: EOF},
+		{data: dat, off: 0, n: len(dat) + 2, bufLen: len(dat), at: 0, exp: dat, err: nil},
+		{data: dat, off: 0, n: len(dat), bufLen: len(dat) / 2, at: 0, exp: dat[:len(dat)/2], err: nil},
+		{data: dat, off: 0, n: len(dat), bufLen: len(dat), at: 0, exp: dat, err: nil},
+		{data: dat, off: 0, n: len(dat), bufLen: len(dat) / 2, at: 2, exp: dat[2 : 2+len(dat)/2], err: nil},
+		{data: dat, off: 3, n: len(dat), bufLen: len(dat) / 2, at: 2, exp: dat[5 : 5+len(dat)/2], err: nil},
+		{data: dat, off: 3, n: len(dat) / 2, bufLen: len(dat)/2 - 2, at: 2, exp: dat[5 : 5+len(dat)/2-2], err: nil},
+		{data: dat, off: 3, n: len(dat) / 2, bufLen: len(dat)/2 + 2, at: 2, exp: dat[5 : 5+len(dat)/2-2], err: EOF},
+		{data: dat, off: 0, n: 0, bufLen: 0, at: -1, exp: "", err: EOF},
+		{data: dat, off: 0, n: 0, bufLen: 0, at: 1, exp: "", err: EOF},
+	}
+	for i, tt := range tests {
+		r := strings.NewReader(tt.data)
+		s := NewSectionReader(r, int64(tt.off), int64(tt.n))
+		buf := make([]byte, tt.bufLen)
+		if n, err := s.ReadAt(buf, int64(tt.at)); n != len(tt.exp) || string(buf[:n]) != tt.exp || err != tt.err {
+			t.Fatalf("%d: ReadAt(%d) = %q, %v; expected %q, %v", i, tt.at, buf[:n], err, tt.exp, tt.err)
+		}
+		if _r, off, n := s.Outer(); _r != r || off != int64(tt.off) || n != int64(tt.n) {
+			t.Fatalf("%d: Outer() = %v, %d, %d; expected %v, %d, %d", i, _r, off, n, r, tt.off, tt.n)
+		}
+	}
+}
+
+func TestSectionReader_Seek(t *testing.T) {
+	// Verifies that NewSectionReader's Seeker behaves like bytes.NewReader (which is like strings.NewReader)
+	br := bytes.NewReader([]byte("foo"))
+	sr := NewSectionReader(br, 0, int64(len("foo")))
+
+	for _, whence := range []int{SeekStart, SeekCurrent, SeekEnd} {
+		for offset := int64(-3); offset <= 4; offset++ {
+			brOff, brErr := br.Seek(offset, whence)
+			srOff, srErr := sr.Seek(offset, whence)
+			if (brErr != nil) != (srErr != nil) || brOff != srOff {
+				t.Errorf("For whence %d, offset %d: bytes.Reader.Seek = (%v, %v) != SectionReader.Seek = (%v, %v)",
+					whence, offset, brOff, brErr, srErr, srOff)
+			}
+		}
+	}
+
+	// And verify we can just seek past the end and get an EOF
+	got, err := sr.Seek(100, SeekStart)
+	if err != nil || got != 100 {
+		t.Errorf("Seek = %v, %v; want 100, nil", got, err)
+	}
+
+	n, err := sr.Read(make([]byte, 10))
+	if n != 0 || err != EOF {
+		t.Errorf("Read = %v, %v; want 0, EOF", n, err)
+	}
+}
+
+func TestSectionReader_Size(t *testing.T) {
+	tests := []struct {
+		data string
+		want int64
+	}{
+		{"a long sample data, 1234567890", 30},
+		{"", 0},
+	}
+
+	for _, tt := range tests {
+		r := strings.NewReader(tt.data)
+		sr := NewSectionReader(r, 0, int64(len(tt.data)))
+		if got := sr.Size(); got != tt.want {
+			t.Errorf("Size = %v; want %v", got, tt.want)
+		}
+	}
+}
+
+func TestSectionReader_Max(t *testing.T) {
+	r := strings.NewReader("abcdef")
+	const maxint64 = 1<<63 - 1
+	sr := NewSectionReader(r, 3, maxint64)
+	n, err := sr.Read(make([]byte, 3))
+	if n != 3 || err != nil {
+		t.Errorf("Read = %v %v, want 3, nil", n, err)
+	}
+	n, err = sr.Read(make([]byte, 3))
+	if n != 0 || err != EOF {
+		t.Errorf("Read = %v, %v, want 0, EOF", n, err)
+	}
+	if _r, off, n := sr.Outer(); _r != r || off != 3 || n != maxint64 {
+		t.Fatalf("Outer = %v, %d, %d; expected %v, %d, %d", _r, off, n, r, 3, int64(maxint64))
+	}
+}
+
+// largeWriter returns an invalid count that is larger than the number
+// of bytes provided (issue 39978).
+type largeWriter struct {
+	err error
+}
+
+func (w largeWriter) Write(p []byte) (int, error) {
+	return len(p) + 1, w.err
+}
+
+func TestCopyLargeWriter(t *testing.T) {
+	want := ErrInvalidWrite
+	rb := new(Buffer)
+	wb := largeWriter{}
+	rb.WriteString("hello, world.")
+	if _, err := Copy(wb, rb); err != want {
+		t.Errorf("Copy error: got %v, want %v", err, want)
+	}
+
+	want = errors.New("largeWriterError")
+	rb = new(Buffer)
+	wb = largeWriter{err: want}
+	rb.WriteString("hello, world.")
+	if _, err := Copy(wb, rb); err != want {
+		t.Errorf("Copy error: got %v, want %v", err, want)
+	}
+}
+
+func TestNopCloserWriterToForwarding(t *testing.T) {
+	for _, tc := range [...]struct {
+		Name string
+		r    Reader
+	}{
+		{"not a WriterTo", Reader(nil)},
+		{"a WriterTo", struct {
+			Reader
+			WriterTo
+		}{}},
+	} {
+		nc := NopCloser(tc.r)
+
+		_, expected := tc.r.(WriterTo)
+		_, got := nc.(WriterTo)
+		if expected != got {
+			t.Errorf("NopCloser incorrectly forwards WriterTo for %s, got %t want %t", tc.Name, got, expected)
+		}
+	}
+}
+
+func TestOffsetWriter_Seek(t *testing.T) {
+	tmpfilename := "TestOffsetWriter_Seek"
+	tmpfile, err := os.CreateTemp(t.TempDir(), tmpfilename)
+	if err != nil || tmpfile == nil {
+		t.Fatalf("CreateTemp(%s) failed: %v", tmpfilename, err)
+	}
+	defer tmpfile.Close()
+	w := NewOffsetWriter(tmpfile, 0)
+
+	// Should throw error errWhence if whence is not valid
+	t.Run("errWhence", func(t *testing.T) {
+		for _, whence := range []int{-3, -2, -1, 3, 4, 5} {
+			var offset int64 = 0
+			gotOff, gotErr := w.Seek(offset, whence)
+			if gotOff != 0 || gotErr != ErrWhence {
+				t.Errorf("For whence %d, offset %d, OffsetWriter.Seek got: (%d, %v), want: (%d, %v)",
+					whence, offset, gotOff, gotErr, 0, ErrWhence)
+			}
+		}
+	})
+
+	// Should throw error errOffset if offset is negative
+	t.Run("errOffset", func(t *testing.T) {
+		for _, whence := range []int{SeekStart, SeekCurrent} {
+			for offset := int64(-3); offset < 0; offset++ {
+				gotOff, gotErr := w.Seek(offset, whence)
+				if gotOff != 0 || gotErr != ErrOffset {
+					t.Errorf("For whence %d, offset %d, OffsetWriter.Seek got: (%d, %v), want: (%d, %v)",
+						whence, offset, gotOff, gotErr, 0, ErrOffset)
+				}
+			}
+		}
+	})
+
+	// Normal tests
+	t.Run("normal", func(t *testing.T) {
+		tests := []struct {
+			offset    int64
+			whence    int
+			returnOff int64
+		}{
+			// keep in order
+			{whence: SeekStart, offset: 1, returnOff: 1},
+			{whence: SeekStart, offset: 2, returnOff: 2},
+			{whence: SeekStart, offset: 3, returnOff: 3},
+			{whence: SeekCurrent, offset: 1, returnOff: 4},
+			{whence: SeekCurrent, offset: 2, returnOff: 6},
+			{whence: SeekCurrent, offset: 3, returnOff: 9},
+		}
+		for idx, tt := range tests {
+			gotOff, gotErr := w.Seek(tt.offset, tt.whence)
+			if gotOff != tt.returnOff || gotErr != nil {
+				t.Errorf("%d:: For whence %d, offset %d, OffsetWriter.Seek got: (%d, %v), want: (%d, <nil>)",
+					idx+1, tt.whence, tt.offset, gotOff, gotErr, tt.returnOff)
+			}
+		}
+	})
+}
+
+func TestOffsetWriter_WriteAt(t *testing.T) {
+	const content = "0123456789ABCDEF"
+	contentSize := int64(len(content))
+	tmpdir, err := os.MkdirTemp(t.TempDir(), "TestOffsetWriter_WriteAt")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	work := func(off, at int64) {
+		position := fmt.Sprintf("off_%d_at_%d", off, at)
+		tmpfile, err := os.CreateTemp(tmpdir, position)
+		if err != nil || tmpfile == nil {
+			t.Fatalf("CreateTemp(%s) failed: %v", position, err)
+		}
+		defer tmpfile.Close()
+
+		var writeN int64
+		var wg sync.WaitGroup
+		// Concurrent writes, one byte at a time
+		for step, value := range []byte(content) {
+			wg.Add(1)
+			go func(wg *sync.WaitGroup, tmpfile *os.File, value byte, off, at int64, step int) {
+				defer wg.Done()
+
+				w := NewOffsetWriter(tmpfile, off)
+				n, e := w.WriteAt([]byte{value}, at+int64(step))
+				if e != nil {
+					t.Errorf("WriteAt failed. off: %d, at: %d, step: %d\n error: %v", off, at, step, e)
+				}
+				atomic.AddInt64(&writeN, int64(n))
+			}(&wg, tmpfile, value, off, at, step)
+		}
+		wg.Wait()
+
+		// Read one more byte to reach EOF
+		buf := make([]byte, contentSize+1)
+		readN, err := tmpfile.ReadAt(buf, off+at)
+		if err != EOF {
+			t.Fatalf("ReadAt failed: %v", err)
+		}
+		readContent := string(buf[:contentSize])
+		if writeN != int64(readN) || writeN != contentSize || readContent != content {
+			t.Fatalf("%s:: WriteAt(%s, %d) error. \ngot n: %v, content: %s \nexpected n: %v, content: %v",
+				position, content, at, readN, readContent, contentSize, content)
+		}
+	}
+	for off := int64(0); off < 2; off++ {
+		for at := int64(0); at < 2; at++ {
+			work(off, at)
+		}
+	}
+}
+
+func TestWriteAt_PositionPriorToBase(t *testing.T) {
+	tmpdir := t.TempDir()
+	tmpfilename := "TestOffsetWriter_WriteAt"
+	tmpfile, err := os.CreateTemp(tmpdir, tmpfilename)
+	if err != nil {
+		t.Fatalf("CreateTemp(%s) failed: %v", tmpfilename, err)
+	}
+	defer tmpfile.Close()
+
+	// start writing position in OffsetWriter
+	offset := int64(10)
+	// position we want to write to the tmpfile
+	at := int64(-1)
+	w := NewOffsetWriter(tmpfile, offset)
+	_, e := w.WriteAt([]byte("hello"), at)
+	if e == nil {
+		t.Errorf("error expected to be not nil")
+	}
+}
+
+func TestOffsetWriter_Write(t *testing.T) {
+	const content = "0123456789ABCDEF"
+	contentSize := len(content)
+	tmpdir := t.TempDir()
+
+	makeOffsetWriter := func(name string) (*OffsetWriter, *os.File) {
+		tmpfilename := "TestOffsetWriter_Write_" + name
+		tmpfile, err := os.CreateTemp(tmpdir, tmpfilename)
+		if err != nil || tmpfile == nil {
+			t.Fatalf("CreateTemp(%s) failed: %v", tmpfilename, err)
+		}
+		return NewOffsetWriter(tmpfile, 0), tmpfile
+	}
+	checkContent := func(name string, f *os.File) {
+		// Read one more byte to reach EOF
+		buf := make([]byte, contentSize+1)
+		readN, err := f.ReadAt(buf, 0)
+		if err != EOF {
+			t.Fatalf("ReadAt failed, err: %v", err)
+		}
+		readContent := string(buf[:contentSize])
+		if readN != contentSize || readContent != content {
+			t.Fatalf("%s error. \ngot n: %v, content: %s \nexpected n: %v, content: %v",
+				name, readN, readContent, contentSize, content)
+		}
+	}
+
+	var name string
+	name = "Write"
+	t.Run(name, func(t *testing.T) {
+		// Write directly (off: 0, at: 0)
+		// Write content to file
+		w, f := makeOffsetWriter(name)
+		defer f.Close()
+		for _, value := range []byte(content) {
+			n, err := w.Write([]byte{value})
+			if err != nil {
+				t.Fatalf("Write failed, n: %d, err: %v", n, err)
+			}
+		}
+		checkContent(name, f)
+
+		// Copy -> Write
+		// Copy file f to file f2
+		name = "Copy"
+		w2, f2 := makeOffsetWriter(name)
+		defer f2.Close()
+		Copy(w2, f)
+		checkContent(name, f2)
+	})
+
+	// Copy -> WriteTo -> Write
+	// Note: strings.Reader implements the io.WriterTo interface.
+	name = "Write_Of_Copy_WriteTo"
+	t.Run(name, func(t *testing.T) {
+		w, f := makeOffsetWriter(name)
+		defer f.Close()
+		Copy(w, strings.NewReader(content))
+		checkContent(name, f)
+	})
+}