I very definitely write code as part of my design process. Code is free. It's not like building a shed where nailing some boards together to see how a truss should work costs money. Banging on some keys to see how sockets should interplay is free (disregarding time, but we're already engaged in "design", and I presume we are interested in "the right answer, sometime" instead of "the wrong answer, today"). So I code as part of my design process. I might throw that code away. I might keep a function or five. Who knows? But there is no way to know what the design is going to look like until you know all of the limitations, and the only way to know all of the limitations is to actually take a peek.