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) {
	r := NewReader([]byte("世界"))
	if _, _, err := r.ReadRune(); err != nil {
		t.Errorf("ReadRune: unexpected error: %v", err)
	}

	const want = "abcdef"
	r.Reset([]byte(want))

				}
				t.Logf("read(%d) = %q, %v", len(p), string(p[:n]), err)
			}
			want("abc", nil)
			want("", nil)
			want("def", nil)
			want("", io.EOF)
		})
	}
}

func TestReaderReset(t *testing.T) {
	checkAll := func(r *Reader, want string) {
		t.Helper()
		all, err := io.ReadAll(r)
		if err != nil {
			t.Fatal(err)
		}
		if string(all) != want {