`timescale 1ns/1ps

module tb_blink;

reg clk;
wire led;

blink DUT(
    .clk(clk),
    .led(led)
);

// Clock generator (50 MHz)
always #10 clk = ~clk;

// Self checking logic
integer error_count = 0;
reg led_prev;

initial begin
    clk = 0;
    led_prev = 0;

    #100000; // simulate time

    if(error_count == 0)
        $display("SELF CHECK PASSED");
    else
        $display("SELF CHECK FAILED, errors = %d", error_count);

    $stop;
end

// Check LED toggle behavior
always @(posedge clk)
begin
    #1;
    if(led == led_prev)
        error_count = error_count + 1;

    led_prev = led;
end

endmodule