How would I make an function/equation to test the circuit?

Sorry but most of the parts you have chosen do not have simulation models associated with them. Please refer to: https://easyeda.com/forum/topic/How_to_find_simulatable_parts_in_EasyEDA-1YgasK2kC It is beyound the scope of spice simulation to model complex digital functions such as an Arduino board. You must simplify the interfaces to such a board to something that can be modelled using basic spice elements such as PULSE or PWL voltage sources and simple logic gating. EasyEDA does have several higher level logic device models but they are still pretty basic parts. You will find all the EasyEDA logic parts by following the link above.