want = strconv.AppendInt(want, int64(i), 10)
		got.Write(b)
	}
	if !Equal(got.Bytes(), want) {
		t.Fatalf("Bytes() = %q, want %q", &got, want)
	}

	// With a sufficiently sized buffer, there should be no allocations.
	n := testing.AllocsPerRun(100, func() {
		got.Reset()
		for i := 0; i < 1000; i++ {
			b := got.AvailableBuffer()
			b = strconv.AppendInt(b, int64(i), 10)
			got.Write(b)
		}
	})

			}
			if b != data[i] {
				t.Fatalf("n = %d: incorrect byte returned from ReadByte: got %q, want %q", n, b, data[i])
			}
		}
		// Unread one byte if there is one.
		if n > 0 {
			if err := r.UnreadByte(); err != nil {
				t.Errorf("n = %d: unexpected error on UnreadByte: %v", n, err)
			}
		}
		// Test that we cannot unread any further.

	n := copy(b.buf[b.n:], s)
	b.n += n
	nn += n
	return nn, nil
}

// ReadFrom implements [io.ReaderFrom]. If the underlying writer
// supports the ReadFrom method, this calls the underlying ReadFrom.
// If there is buffered data and an underlying ReadFrom, this fills
// the buffer and writes it before calling ReadFrom.
func (b *Writer) ReadFrom(r io.Reader) (n int64, err error) {
	if b.err != nil {
		return 0, b.err
	}

			PAXRecords: map[string]string{
				"linkpath": "PAX4/PAX4/long-linkpath-name",
			},
			Format: FormatPAX,
		}},
	}, {
		// Both BSD and GNU tar truncate long names at first NUL even
		// if there is data following that NUL character.
		// This is reasonable as GNU long names are C-strings.
		file: "testdata/gnu-long-nul.tar",
		headers: []*Header{{
			Name:     "0123456789",
			Mode:     0644,