What's the best way to virtually design and test your circuits?
If you are asking this question, I think designing ICs may be jumping a bit too far into the deep end as the first step.

For virtually testing circuits, consider simulation software such as a VHDL/Verilog simulator (for logic) or Spice (for analog).

When you say "tested in BASIC", I would interpret that as "simulated using a simulator written in BASIC".