A programmable square$-$wave generator produces a square wave with variable on $($logic $1)$ and off $($logic $0)$ intervals. The durations of the high and low intervals are specified by $3-$bit unsigned integer parameters M and N$,$ representing M x $10$ ns and N x $10$ ns$,$ respectively. Write a verilog module for this programmable square$-$wave generator. Write a testbench for your design to verify its functionality.