(1) You have unconnected ports on the entity you are typing to test. The test results are as expected for those inputs - specifically, clk, being undriven.
(2) Having connected clk, you will need to drive it.
signal clk : std_logic := '0';
and
clk <= not clk after 50 ns;
should give a 10MHz clock, check this in the simulator
(3) Drive "KEY" with a specific sequence of values
subtype keys is std_logic_vector(3 downto 0);
constant count_up : keys := "0001";
constant count_dn : keys := "0010";
constant idle : keys := "0000";
-- etc
process
begin
KEY <= count_up;
wait for 1 us;
KEY <= idle;
wait for ...
-- etc
end process;
(4) Bring the OUTPUTS back out into the testbench so that you can check their values. You need to bring them out as ports in the top level (design) entity anyway, if you are going to connect them to a display!
Then (later, once things have started going to plan) you can test them in the testbench process...
wait for 100 ns;
-- after the last press, we should have "07" on the display
assert digit(1) = "0111111" report "Left digit has wrong value" severity ERROR;
assert digit(0) = "0000111" report "Left digit has wrong value" severity ERROR;
A self-checking testbench like this saves debugging by staring at waveforms. You only need the waveforms when the tests are failing...