Best bech template for kick start:

--#############################################################################
-- Entity

library ieee;
use ieee.std_logic_1164.all;

entity tb is
end entity;


--#############################################################################
-- Architecture

library ieee;
use ieee.numeric_std.all;

architecture sim of tb is

  --===========================================================================
  -- Clock and reset decl.

  -- Clock
  constant CLK_FREQ : real := 100.0E6;  -- Clock frequency in Hz
  signal clk        : std_logic;

  -- Reset
  constant RST_PER : time := 100 ns;    -- Reset period; and then waiting for rising clk edge before deassert rst
  signal rst       : std_logic;


  --===========================================================================
  -- Device Under Test (DUT) decl.

  signal dut_address  : integer range 0 to 15;
  signal dut_data_out : std_logic_vector(7 downto 0);


  --===========================================================================
  -- Test control decl.

  -- None


begin


  --===========================================================================
  -- Clock and reset impl.

  -- Clock generation
  process is
  begin
    while true loop
      clk <= '1';
      wait for 0.5 sec / CLK_FREQ;
      clk <= '0';
      wait for (1.0 sec / CLK_FREQ) - (0.5 sec / CLK_FREQ);
    end loop;
  end process;

  -- Reset generation
  process is
  begin
    rst <= '1';
    wait for RST_PER;
    wait until rising_edge(clk);
    rst <= '0';
    wait;
  end process;


  --===========================================================================
  -- Device Under Test (DUT) impl.

  rom_e : entity work.rom
    port map(
      address  => dut_address,
      data_out => dut_data_out);


  --===========================================================================
  -- Test control general

  process is
  begin
    -- Wait for reset release and clock.
    wait until rst = '0';
    wait until rising_edge(clk);
    -- Address apply and data output check
    for address in 0 to 15 loop
      wait until rising_edge(clk);
      dut_address <= address;
      wait until rising_edge(clk);
      -- Check output of ROM
    end loop;
    -- Run for a while
    wait for 1 us;
    -- End of simulation
    report "OK   ########## Sim end: OK :-) ##########   (not actual failure)" severity failure;
    wait;
  end process;

end architecture;


--#############################################################################
-- EOF