Escribiendo testbench para el diseño de VHDL

He hecho un banco de pruebas simple para ROM. Me gustaría escribir un banco de pruebas para una pantalla VGA. Soy un poco principiante, así que no sé cómo escribirlo. Sé que necesito generar un reloj, pero ¿cómo generaría los contadores, etc.? ¡Muchas gracias! Aquí está mi diseño vhdl

  library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;


entity VGA_display is
          port (
            -- Assuming 50MHz clock.If the clock is reduced then it might give the unexpected output.      
                  clock: in std_logic;

             -- The counter tells whether the correct position on the screen is reached where the data is to be displayed. 
                  hcounter: in integer range 0 to 1023;
                  vcounter: in integer range 0 to 1023;

          -- Output the colour that should appear on the screen. 
                  pixels : out std_logic_vector(7 downto 0)               
                );
end VGA_display;

architecture Behavioral of VGA_display is   
    -- Intermediate register telling the exact position on display on screen.
         signal x : integer range 0 to 1023 := 100;
         signal y : integer range 0 to 1023 := 80;
         signal addr: INTEGER RANGE 0 TO 15;
         signal pix: STD_LOGIC_VECTOR(7 DOWNTO 0);
                   -- Clock period definitions
         constant Clk_period : time := 10 ns;

begin


      rom1: entity work.rom port map(address => addr, data_out => pix, clk => clock);



 -- On every positive edge of the clock counter condition is checked,
  output1: process(clock)
              begin
                    if rising_edge (clock) then

                    -- If the counter satisfy the condition, then output the colour that should appear.
                        if (hcounter >= 1)  and (hcounter < 128) and (vcounter >= 1) and (vcounter < 128
                               ) then

                           addr <= vcounter * 128 + hcounter;

                           pixels <= pix; 

                    -- If the condition is not satisfied then the output colour will be black.
                        else 
                          pixels <= x"00";
                        end if;
              end if;
           end process;
end Behavioral;