The character count everyone quotes is a proxy. Google truncates on rendered width, not character count, which is why two descriptions of identical length can truncate differently.
Width varies per character
In a proportional typeface, i and l are narrow while m and W are wide. A 160-character description of mostly narrow letters can render shorter than a 150-character one full of capitals. The real desktop budget is roughly 920 pixels; character counts are a convenient approximation of it.
Google rewrites you anyway
A substantial share of displayed descriptions are not the ones in the markup. Google frequently substitutes text from the page body when it judges that a better match for the query. Optimising length is worthwhile; assuming your text will be shown verbatim is not.
What to validate in a build pipeline
Check presence, uniqueness across the site, and a sane length band. Uniqueness is the one worth failing a build over — a duplicate description across hundreds of URLs is a template bug, and it is far more damaging than a description that runs ten characters long.
Try it: Meta Description Length Checker on SeoWolf's Notepad.