Add a simple unit test for widget_add_from_file()

unittest/mgos_mock.h

@@ -4,9 +4,9 @@
 /* Some functions mocked from MGOS, so we can run unit tests standalone.
  */
 
-#include <stdio.h>
-#include <string.h>
+#include "mgos.h"
 
+// mgos_log
 enum cs_log_level {
   LL_NONE = -1,
   LL_ERROR = 0,
@@ -27,4 +27,13 @@ int log_print_prefix(enum cs_log_level l, const char *func, const char *file);
     printf("\r\n"); \
   } while (0)
 
+
+// mgos_timer
+#define MGOS_TIMER_REPEAT 1
+typedef uintptr_t mgos_timer_id;
+typedef void (*timer_callback)(void *param);
+
+mgos_timer_id mgos_set_timer(int msecs, int flags, timer_callback cb, void *cb_arg);
+void mgos_clear_timer(mgos_timer_id id);
+
 #endif // __MGOS_MOCK_H