--- tests/check_money.3.c	2020-06-21 15:52:50.000000000 +0000
+++ tests/check_money.6.c	2020-06-21 15:52:50.000000000 +0000
@@ -1,65 +1,94 @@
 /*
  * Check: a unit test framework for C
  * Copyright (C) 2001, 2002 Arien Malec
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with this library; if not, write to the
  * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
  * MA 02110-1301, USA.
  */
 
 #include <stdlib.h>
 #include <check.h>
 #include "../src/money.h"
 
 START_TEST(test_money_create)
 {
     Money *m;
 
     m = money_create(5, "USD");
     ck_assert_int_eq(money_amount(m), 5);
     ck_assert_str_eq(money_currency(m), "USD");
     money_free(m);
 }
 END_TEST
 
+START_TEST(test_money_create_neg)
+{
+    Money *m = money_create(-1, "USD");
+
+    ck_assert_msg(m == NULL,
+                  "NULL should be returned on attempt to create with "
+                  "a negative amount");
+}
+END_TEST
+
+START_TEST(test_money_create_zero)
+{
+    Money *m = money_create(0, "USD");
+
+    if (money_amount(m) != 0)
+    {
+        ck_abort_msg("Zero is a valid amount of money");
+    }
+}
+END_TEST
+
 Suite * money_suite(void)
 {
     Suite *s;
     TCase *tc_core;
+    TCase *tc_limits;
 
     s = suite_create("Money");
 
     /* Core test case */
     tc_core = tcase_create("Core");
 
     tcase_add_test(tc_core, test_money_create);
     suite_add_tcase(s, tc_core);
 
+    /* Limits test case */
+    tc_limits = tcase_create("Limits");
+
+    tcase_add_test(tc_limits, test_money_create_neg);
+    tcase_add_test(tc_limits, test_money_create_zero);
+    suite_add_tcase(s, tc_limits);
+
     return s;
 }
 
 int main(void)
 {
     int number_failed;
     Suite *s;
     SRunner *sr;
 
     s = money_suite();
     sr = srunner_create(s);
 
     srunner_run_all(sr, CK_NORMAL);
     number_failed = srunner_ntests_failed(sr);
     srunner_free(sr);
     return (number_failed == 0) ? EXIT_SUCCESS : EXIT_FAILURE;
 }