demo of how core dumps don't appear on macOS 10.13 for me

macos-10_13-no-cores.txt

[~]
$ sw_vers
ProductName:	Mac OS X
ProductVersion:	10.13.6
BuildVersion:	17G4015
[~]
$ ulimit -a
-t: cpu time (seconds)              unlimited
-f: file size (blocks)              unlimited
-d: data seg size (kbytes)          unlimited
-s: stack size (kbytes)             8192
-c: core file size (blocks)         unlimited
-v: address space (kbytes)          unlimited
-l: locked-in-memory size (kbytes)  unlimited
-u: processes                       2837
-n: file descriptors                7168
[~]
$ ls -ld /cores
drwxrwxr-t@ 2 root  admin  64 Jan 20 19:02 /cores
[~]
$ touch /cores/test
[~]
$ ls -l /cores/test
-rw-r--r--  1 janke  admin  0 Jan 20 19:02 /cores/test
[~]
$ sleep 100 &
[1] 28515
[~]
$ killall -SIGSEGV sleep
[1]  + 28515 segmentation fault  sleep 100
[~]
$ ls -a /cores
.    ..   test
[~]
$