// This stuff just sets up the proper time scale and format for the
// simulation, for now do not modify.
`timescale 1ns/10ps
/*module timeunit;
   initial $timeformat(-9,1," ns",9);
endmodule*/

 
// Here is the testbench proper:
module counter_testbench ( ) ;
 
    // Test bench gets wires for all device under test (DUT) outputs:
   
   wire [3:0]        out;
 
   // Regs for all DUT inputs:
   reg               clk;
   reg               reset;
 
 
   counter dut (// (dut means device under test)
                // Outputs
                .out            (out[3:0]),
                // Inputs
                .reset          (reset),
                .clk            (clk));
 

  // Setup clk to automatically strobe with a period of 20.
   always #10 clk = ~clk;

    
   initial
     begin

        // First setup up to monitor all inputs and outputs
        $monitor ("time=%5d ns, clk=%b, reset=%b, out=%b", $time, clk, reset, out[3:0]);
        
        // First initialize all registers
        clk = 1'b0;             // what happens to clk if we don't 
                                // set this?;
        reset = 1'b0;
     
        @(posedge clk);#1;      // this  says wait for rising edge 
                                // of clk and one more tic (to prevent
                                // shoot through)

        reset = 1'b1;
        
        @(posedge clk);#1;

        reset = 1'b0;

        // Lets watch what happens after 7 cycles
        @(posedge clk);#1;        
        @(posedge clk);#1;        
        @(posedge clk);#1;        
        @(posedge clk);#1;        
        @(posedge clk);#1;        
        @(posedge clk);#1;        
        @(posedge clk);#1;        
        
        
        // At this point we should have a 4'b0110 coming out out because
        // the counter should have counted for 7 cycles from 0
        if (out != 4'b0110) begin
           $display("ERROR 1: Out is not equal to 4'b0110");
           $finish;
        end
        
        
        // We got this far so all tests passed.
        $display("All tests completed successfully\n\n");
        
        $finish;
     end
   
   
   // This is to create a dump file for offline viewing.
   initial
     begin
        $dumpfile ("counter.dump");
        $dumpvars (0, counter_testbench);
     end // initial begin
   
   
endmodule // counter_testbench