tb: make uart selftesting

- Exit with the right exit code

hw/application_fpga/core/uart/tb/tb_uart.v

@@ -324,6 +324,23 @@ module tb_uart ();
   endtask  // display_test_result
 
 
+  //----------------------------------------------------------------
+  // exit_with_error_code()
+  //
+  // Exit with the right error code
+  //----------------------------------------------------------------
+  task exit_with_error_code;
+    begin
+      if (error_ctr == 0) begin
+        $finish(0);
+      end
+      else begin
+        $fatal(1);
+      end
+    end
+  endtask  // exit_with_error_code
+
+
   //----------------------------------------------------------------
   // uart_test
   // The main test functionality.
@@ -340,7 +357,7 @@ module tb_uart ();
 
     display_test_result();
     $display("*** Simulation done.");
-    $finish;
+    exit_with_error_code();
   end  // uart_test
 endmodule  // tb_uart