b := NewWriterSize(tw, BufSize)
		b.WriteString("abc")
		tw.check(t, "", "")
		b.WriteString("123456789012345")      // long string, non-empty buffer
		tw.check(t, "abc12345", "6789012345") // use Write and then WriteString since the remaining part is still longer than BufSize
	}
	{
		tw := &teststringwriter{}
		b := NewWriterSize(tw, BufSize)
		b.Write([]byte("abc")) // same as above, but use Write instead of WriteString

	const keep = 10
	ss := &suffixSaver{keep: keep}
	ss.Write([]byte("abc"))
	if got := string(ss.Suffix()); got != "abc" {
		t.Errorf("got = %q; want abc", got)
	}
	ss.Write([]byte("defghijklmno"))
	if got := string(ss.Suffix()); got != "fghijklmno" {
		t.Errorf("got = %q; want fghijklmno", got)
	}
	if got, want := ss.Size(), int64(len("abc")+len("defghijklmno")); got != want {
		t.Errorf("Size = %d; want %d", got, want)

		wantRes string
		wantKey string
		wantVal string
		ok      bool
	}{
		{"6 k=v\n\n", "\n", "k", "v", true},
		{"19 path=/etc/hosts\n", "", "path", "/etc/hosts", true},
		{"210 path=" + longName + "\nabc", "abc", "path", longName, true},
		{"110 path=" + medName + "\n", "", "path", medName, true},
		{"9 foo=ba\n", "", "foo", "ba", true},
		{"11 foo=bar\n\x00", "\x00", "foo", "bar", true},

		t.Errorf("behavior differs: with = %#v; without: %#v", with, withOut)
	}
}

// tests that Len is affected by reads, but Size is not.
func TestReaderLenSize(t *testing.T) {
	r := NewReader([]byte("abc"))
	io.CopyN(io.Discard, r, 1)
	if r.Len() != 2 {
		t.Errorf("Len = %d; want 2", r.Len())
	}
	if r.Size() != 3 {
		t.Errorf("Size = %d; want 3", r.Size())
	}
}

func TestReaderReset(t *testing.T) {

string_lit             = raw_string_lit | interpreted_string_lit .
raw_string_lit         = "`" { unicode_char | newline } "`" .
interpreted_string_lit = `"` { unicode_value | byte_value } `"` .
</pre>

<pre>
`abc`                // same as "abc"
`\n
\n`                  // same as "\\n\n\\n"
"\n"
"\""                 // same as `"`
"Hello, world!\n"
"日本語"
"\u65e5本\U00008a9e"
"\xff\u00FF"

string_lit             = raw_string_lit | interpreted_string_lit .
raw_string_lit         = "`" { unicode_char | newline } "`" .
interpreted_string_lit = `"` { unicode_value | byte_value } `"` .
</pre>

<pre>
`abc`                // same as "abc"
`\n
\n`                  // same as "\\n\n\\n"
"\n"
"\""                 // same as `"`
"Hello, world!\n"
"日本語"
"\u65e5本\U00008a9e"
"\xff\u00FF"

	}
}

var cutTests = []struct {
	s, sep        string
	before, after string
	found         bool
}{
	{"abc", "b", "a", "c", true},
	{"abc", "a", "", "bc", true},
	{"abc", "c", "ab", "", true},
	{"abc", "abc", "", "", true},
	{"abc", "", "", "abc", true},
	{"abc", "d", "abc", "", false},
	{"", "d", "", "", false},
	{"", "", "", "", true},
}

func TestCut(t *testing.T) {

}

func ExampleToValidUTF8() {
	fmt.Printf("%s\n", bytes.ToValidUTF8([]byte("abc"), []byte("\uFFFD")))
	fmt.Printf("%s\n", bytes.ToValidUTF8([]byte("a\xffb\xC0\xAFc\xff"), []byte("")))
	fmt.Printf("%s\n", bytes.ToValidUTF8([]byte("\xed\xa0\x80"), []byte("abc")))
	// Output:
	// abc
	// abc
	// abc
}

func ExampleTrim() {
	fmt.Printf("[%q]", bytes.Trim([]byte(" !!! Achtung! Achtung! !!! "), "! "))

		tests: []testFnc{
			testRead{100, "\x00ab", io.ErrUnexpectedEOF},
		},
	}, {
		maker: makeSparse{makeReg{"abc", 3}, sparseDatas{{1, 3}, {6, 5}}, 15},
		tests: []testFnc{
			testRead{100, "\x00abc\x00\x00", errMissData},
		},
	}, {
		maker: makeSparse{makeReg{"abc", 8}, sparseDatas{{1, 3}, {6, 5}}, 15},
		tests: []testFnc{
			testRead{100, "\x00abc\x00\x00", io.ErrUnexpectedEOF},
		},
	}, {

	a, b []byte
	i    int
}{
	{[]byte(""), []byte(""), 0},
	{[]byte("a"), []byte(""), 1},
	{[]byte(""), []byte("a"), -1},
	{[]byte("abc"), []byte("abc"), 0},
	{[]byte("abd"), []byte("abc"), 1},
	{[]byte("abc"), []byte("abd"), -1},
	{[]byte("ab"), []byte("abc"), -1},
	{[]byte("abc"), []byte("ab"), 1},
	{[]byte("x"), []byte("ab"), 1},
	{[]byte("ab"), []byte("x"), -1},
	{[]byte("x"), []byte("a"), 1},