t.Errorf("got string %q; want %q", b.String(), s)
		}
		if r.Len() != 0 {
			t.Errorf("reader contains %v bytes; want 0", r.Len())
		}
	}
}

func TestReaderLen(t *testing.T) {
	const data = "hello world"
	r := NewReader([]byte(data))
	if got, want := r.Len(), 11; got != want {
		t.Errorf("r.Len(): got %d, want %d", got, want)
	}
	if n, err := r.Read(make([]byte, 10)); err != nil || n != 10 {