fsm_traffic/tb/traffic_light_tb.v

`timescale 1ns/1ns
module traffic_light_tb();
parameter CYCLE = 20;
reg             sys_clk     ;
reg             sys_rst_n   ;
wire [3: 0]     led         ;
always #(CYCLE / 2)  sys_clk = ~sys_clk;
initial begin
    sys_clk     = 1'b0;
    sys_rst_n   = 1'b0;
    #(CYCLE);
    sys_rst_n   = 1'b1;
    #(CYCLE * 5 * 83);//20 x 5 x 83 = 8300ns
    $stop;
end

traffic_light   traffic_light_inst(
.sys_clk        (sys_clk)   ,
.sys_rst_n      (sys_rst_n) ,

.led            (led)
);

defparam traffic_light_inst.MAX_S = 5;//1s-->5 x 20 = 100ns
endmodule