VHDL Module simulation

Hi, I'm new to VHDL and find it difficult to create a testbench for a code. The code will display A5A5 when the input is '00', it will display 12345678ABCDEF when the input is '01', display 500662 when the input is '10' and it will display 503188 '11'. I'm using ISE Project navigator which creates the test bench but I can't get the right parameters to test the code, can anyone guide me on how to proceed about this. The code is below :

  library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity DataGen is
    Port ( Input : in  STD_LOGIC_VECTOR (1 downto 0);
           CLK, Reset : in  STD_LOGIC;
           Output : out  STD_LOGIC_VECTOR (15 downto 0));
     
end DataGen;
architecture Behavioral of DataGen is
signal counter : STD_LOGIC_VECTOR (1 downto 0);
begin
process ( Reset, CLK )
begin 
 if Reset = '1' then -- If the reset button is pressed it clears
 Counter <= "00";   -- the Counter value and sets it to 00
 elsif CLK'event and CLK = '1' then -- Used for Mode 1,2,3; Increments the value of Counter 
  Counter <= counter + '1';    -- each time the CLK singal is 1 therefore creating an endless
  if Counter = "11" then     -- loop for Counter
  else counter <= "00";
  
  end if;
 end if;
 
end process;
process ( Input, CLK, Reset, Counter ) 
begin
 
 if Reset = '1' then -- Resets the 7-segment display if Reset is 1
  Output <= X"0000";
  
 elsif CLK'event and CLK = '1' then
  --Mode 0
  if Input = "00" then --if selected it will display A5A5 
  Output <= X"A5A5";
 
  --Mode 1
  elsif Input = "01" then -- if selected will display 1 to F continously
   case Counter is
  
   when "00" => Output <= X"0123";
   when "01" => Output <= X"4567";
   when "10" => Output <= X"89AB";
   when "11" => Output <= X"CDEF";
   when others => Output <= X"0000";
  
   end case;
  
  -- Mode 2
  elsif Input = "10" then --if selected will display 500662 continously
   case Counter is
  
   when "00" => Output <= X"5006";
   when "01" => Output <= X"6250";
   when "10" => Output <= X"0662";
   when "11" => Output <= X"5006";
   when others => Output <=X"0000";
  
   end case;
 
  -- Mode 3
  elsif Input = "11" then --if selected will display 503188 continously
   case Counter is
  
   when "00" => Output <= X"5031";
   when "01" => Output <= X"8850";
   when "10" => Output <= X"3188";
   when "11" => Output <= X"5031";
   when others => Output <= X"0000";
  
   end case;
  end if;
 end if;
end process;
end Behavioral;
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