Add testbench for the seconds display

NOTE: This doesn't actually compile yet, but it should once changes to
the seconds display are pushed

verification/seconds_display_tb.sv

@@ -0,0 +1,51 @@
+module seconds_display_tb;
+int errors = 0;
+logic [5:0] seconds;
+wire [6:0] display_tens;
+wire [6:0] display_ones;
+
+logic [6:0] expected_tens;
+logic [6:0] expected_ones;
+
+seconds_display Dut(.*);
+initial begin
+    $display("Testing seconds_display");
+    for (seconds=0; seconds<60; seconds++) begin
+        expected_ones = encode_number(seconds % 10);
+        expected_tens = encode_number(seconds /10);
+        #1
+        if (display_ones !== expected_ones) begin
+            errors++;
+            $display("Failed ones test case, displayed = %b, expected = %b",
+                     display_ones,
+                     expected_ones);
+        end
+        else
+        if (display_tens !== expected_tens) begin
+            errors++;
+            $display("Failed tens test case, displayed = %b, expected = %b",
+                     display_tens,
+                     expected_tens);
+        end
+    end
+
+    if (errors == 0)
+        $display("All tests passing");
+end
+
+endmodule
+
+function automatic logic [6:0] encode_number(logic [5:0] num);
+    case (num)
+        0: return 7'b1111110;
+        1: return 7'b0000110;
+        2: return 7'b1101101;
+        3: return 7'b1111001;
+        4: return 7'b0110011;
+        5: return 7'b1011011;
+        6: return 7'b1011111;
+        7: return 7'b1110000;
+        8: return 7'b1111111;
+        9: return 7'b1111011;
+    endcase
+endfunction