Can anyone help me to create a Verilog testbench?

Question

Can anyone help me create a testbench or just the input code for my following code? I'm using XILINX.

module fsmb (input rst,clk,a,
             output reg x);

parameter sta = 2'b00, stb = 2'b01, stc = 2'b10,
          std = 2'b11;

reg[1:0] st, nst;

always @(posedge clk)
begin 
    if (rst)
        st <= 2'b00;
    else
        st <= nst;
end

always @*
begin
    st = nst; x =0'b0;
    case (st)
        sta: if(a) nst = stb;
             else nst = sta;
        stb: if(a) nst = stc;
             else nst = stb; 
        stc: begin 
             if(a) nst = stc;
             else nst = std; 
             x =1'b1;
             end
        std: begin
             if(a) nst = stc;
             else nst = sta;
             x = 1'b1;
             end
        default: nst = sta;
    endcase 
end
endmodule

Answer 1

Testbench 101

1. Create a new module (tb).
2. Create a reg for each input of your DUT.
3. Create a wire for each output of your DUT.
4. Create an instance of your DUT.
5. Connect your regs and wires to your DUT.
6. Generate a clock
7. Drive your other inputs
8. Create checkers for your outputs (I'll leave this up to you).

Example:

module tb;

reg rst,clk,a;
wire x;

initial begin
    clk = 0;
    forever #5 clk = ~clk;
end

initial begin
    rst = 1;
    a = 0;
    #50 rst = 0;
    #50 $finish;
end

fsmb fsmb (
    .clk    (clk),
    .rst    (rst),
    .a      (a),
    .x      (x)
);

endmodule

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Other simple testbench examples are provided on EDA playgound. You can sign up for a free account and look at samples such as: Published Playgounds -> D flip flop