It made hiring devs fun. Trying to explain to people why it was that way, and their insistence that software development doesn't work that way.
That is exactly it for 90% of agency projects. Underquoted to get the deal, a rapid development cycle that leaves the devs feeling dead, and then once that first release is out, you have maybe 1 or 2 small updates and the project is never touched again, or at least not for a year or two.
There is no world where it makes sense to write tests for these projects.
Agency for what?
Every developer/engineer should work in an agency for a while because of the amount of sheer work and lifeline of said work is short, projects are primarily promotions and one and dones in many cases.
What we did at the agency I worked at was try to harvest systems from common work. Landing page systems that then had base code that was testable and common across all, create a content management system that supports agency specifics. Promotions/instant win systems that had common code across all and could live longer than the 3 week promotion, create a prize/promotions system that ran all future promotions and improved AFTER most promotions due to time constraints. Game systems for promotional games / advergaming, after new games and types became common or re-usable etc.
Many times, you have to take an after the ship approach and harvest systems that make sense from the sheer amount of work you are going across hundreds of projects. Where good engineering really comes along on subsequent systems where promotions, projects or games/apps were initially made and proved a need or prototype for how to do future projects quicker and with more robust systems.
Testing and doing code specifically for that campaign may be usable or not, but later you can harvest the good ideas and try to formulate a time saving system for the next, including better testing and backbone/baseline libs/tools/tests etc.
I have worked in agencies 5+ years and game studios 5+ years and both are extremely fast paced, usually the harvesting approach is the one that is workable in very pressurized project environments like that. Initial projects/games/apps etc are harvested for good ideas and the first one might even be more prototype like where testing/continuous integration might not fit in the schedule the first time around, or might not even be clear what to standardize and test until multiple types of those projects it out. Starting out with verbose development on new systems/prototypes/promotions/campaigns/games might not be budget capable or time allowed to do so on the first versions as they might be throwaway after just a few weeks or months. There is a delicate balance in agencies/game studios like that where the product and shipping on time is more important on the first go around as the project timeline and lifeline may be short. Subsequent projects that fit that form are where improvements can be made.