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