Error in testbench

问题:

I'm a beginner to vhdl. I am trying to write a VHDL code to describe the behavior of a traffic light. It has 3 signal outputs Yellow (0), Green (1) and Red (2). Initially the light is yellow. It would be turning to Green after 10ns. Green would turn to red after 40ns and red would come back to yellow after 60ns. The state machine is not having any external input and is a free running machine synchronized by a 10ns clock (total time period = 10ns). Traffic light has an external reset control signal to reset the light to yellow.I need to show the testbench with 2 times reset cases and free running output signals in unsigned decimal format.

The vhdl code runs fine on Forcing clock and by removing the code for rst_process in testbench but the rst_process of test-bench doesn't work as expected(goes undefined in simulation)

This is the main vhdl code

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity traf is
    Port ( clk : in  STD_LOGIC;
           rst : in  STD_LOGIC;
           Green : out  STD_LOGIC;
           Red : out  STD_LOGIC;
           Yellow : out  STD_LOGIC);
end traf;

architecture Behavioral of traf is

signal count:integer range 0 to 10 := 0;
signal state:integer range 0 to 2 := 0;
begin
    process(clk, rst)
    begin
        if(rst = '1') then
            state <= 0;
            Red <= '0';
            Green <= '0';
            Yellow <= '1';
            count <= 0;
        elsif clk'event and clk='1' then
        case state is
        when 0 =>  --Yellow Light
        if(count=1) then
            count <= 0;
            state <= 1;
        else
            count <= (count + 1);
            Red <= '0';
            Green <= '0';
            Yellow <= '1';
        end if;

        when 1 =>  --Green Light
        if(count=4) then
            count <= 0;
            state <= 2;
        else
            count <= count + 1;
            Red <= '0';
            Green <= '1';
            Yellow <= '0';
        end if;

        when 2 =>  --Red Light
        if(count=6) then
            count <= 0;
            state <= 0;
        else
            count <= count + 1;
            Red <= '1';
            Green <= '0';
            Yellow <= '0';
        end if;

        when others =>
            state <= 0;
            count <= 0;
        end case;
        end if;
    end process;
end Behavioral;

This is the testbench code

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity tb is
--    Port ( );
end tb;

architecture Behavioral of tb is
signal clk,rst,Green,Red,Yellow:std_logic;
constant clk_period : time:=10 ns;
component traf is
     Port (  
              clk : in  STD_LOGIC;
              rst : in  STD_LOGIC;
              Green : out  STD_LOGIC;
              Red : out  STD_LOGIC;
              Yellow : out  STD_LOGIC
           );
 end component;
begin
DUT:traf PORT MAP
(
    clk=>clk,
    rst=>rst,
    Green=>Green,
    Red=>Red,
    Yellow=>Yellow
);

clk_process:process
begin
    clk <= '0';
    wait for clk_period/2;
    clk <= '1';
    wait for clk_period/2;
end process;

rst_process:process
begin
    rst <= '0';
    wait for clk_period * 15;

    rst <= '1';
    wait for clk_period;

    rst <= '0';
    wait for clk_period * 50;

    rst <= '1';
    wait for clk_period*2;

    rst <= '0';
    wait;
end proocess;

end Behavioral;