Improve test_strptime_days (#21037)

Use `assert` for checking return value.  Use better formatting for
displaying results.

test/core/test_strptime_days.c

@@ -5,6 +5,10 @@
  * found in the LICENSE file.
  */
 
+// glibc requires _XOPEN_SOURCE to be defined in order to get strptime.
+#define _XOPEN_SOURCE
+
+#include <assert.h>
 #include <time.h>
 #include <stdio.h>
 #include <string.h>
@@ -31,9 +35,14 @@ int main() {
   for (int i = 0; i < sizeof(day_tests) / sizeof(day_tests[0]); ++i) {
     memset(&tm, '\0', sizeof(tm));
     char *ptr = strptime(day_tests[i].input, day_tests[i].format, &tm);
+    assert(ptr);
 
-    printf("%s: %d/%d/%d (%dth DoW, %dth DoY)\n",
-           (ptr != NULL && *ptr == '\0') ? "OK" : "ERR", tm.tm_mon + 1,
-           tm.tm_mday, 1900 + tm.tm_year, tm.tm_wday, tm.tm_yday);
+    printf("%-23s -> %02d/%02d/%4d (%dth DoW, %3dth DoY)\n",
+           day_tests[i].input,
+           tm.tm_mon + 1,
+           tm.tm_mday,
+           1900 + tm.tm_year,
+           tm.tm_wday,
+           tm.tm_yday);
   }
 }

test/core/test_strptime_days.out

@@ -1,12 +1,12 @@
-OK: 1/1/2000 (6th DoW, 0th DoY)
-OK: 3/3/2000 (5th DoW, 62th DoY)
-OK: 9/9/1999 (4th DoW, 251th DoY)
-OK: 5/2/1999 (0th DoW, 121th DoY)
-OK: 5/21/2001 (1th DoW, 140th DoY)
-OK: 1/27/2006 (5th DoW, 26th DoY)
-OK: 5/21/2001 (1th DoW, 140th DoY)
-OK: 7/24/2013 (3th DoW, 204th DoY)
-OK: 1/1/2000 (6th DoW, 0th DoY)
-OK: 1/1/2000 (6th DoW, 0th DoY)
-OK: 5/1/2001 (2th DoW, 120th DoY)
-OK: 2/22/2001 (4th DoW, 52th DoY)
+2000-01-01              -> 01/01/2000 (6th DoW,   0th DoY)
+03/03/00                -> 03/03/2000 (5th DoW,  62th DoY)
+9/9/99                  -> 09/09/1999 (4th DoW, 251th DoY)
+19990502123412          -> 05/02/1999 (0th DoW, 121th DoY)
+2001 20 Mon             -> 05/21/2001 (1th DoW, 140th DoY)
+2006 4 Fri              -> 01/27/2006 (5th DoW,  26th DoY)
+2001 21 Mon             -> 05/21/2001 (1th DoW, 140th DoY)
+2013 29 Wed             -> 07/24/2013 (3th DoW, 204th DoY)
+2000-01-01 08:12:21 AM  -> 01/01/2000 (6th DoW,   0th DoY)
+2000-01-01 08:12:21 PM  -> 01/01/2000 (6th DoW,   0th DoY)
+2001 17 Tue             -> 05/01/2001 (2th DoW, 120th DoY)
+2001 8 Thursday         -> 02/22/2001 (4th DoW,  52th DoY)