Is it worth trying to write tests for the most tightly coupled site in the world?

[FMoW]

Imagine that 90% of your job is merely to triage issues on a very massive, very broken website. Imagine that this website is written in the most tightly coupled, least cohesive PHP code you've ever seen, the type of code that would add the original developers to your "slap on sight" list. Imagine that this web application is made up of 4 very disparate parts (1 commercial, 2 "repurposed", and 1 custom) and a crap-ton of virtual duct tape and shims. Imagine that it contains the type of programming practices in which major components of the website actually rely on things NOT working properly, and fixing these broken things usually breaks other things. Imagine that you know from too many bad experiences that changing one seemingly innocuous part of the website, such as splitting a "name" field into two separate "first" and "last" fields, will bring the site to its knees and require hours of rollbacks, merges and patches. Imagine pleading with the customer for years to just ditch the code and start all over but being met with Enterprise-Grade despair and hand wringing. Then imagine getting ASAP/EMERGENCY tickets to implement new features that in any other web site would take 4 hours but you know better with this site so you quote 40 hours, then blow right by that and bill 80 hours, but it's OK because the client is used to that with their website.Here are some other things that you should also imagine:

• there are no tests at all right now
• there are googleteen different layers of logins. Some customers actually have 3 different accounts for different sections of the website
• when I say "tightly coupled", I mean the loops of include/require statements would probably map out like a celtic knot
• when I say "least cohesive" I mean some stuff is organized sort of like MVC, but it's not really MVC. In some cases it may take you several hours just to find out how URI A is mapped to file B
• the UI was written like "obtrusive" and "inaccessible" were the buzzwords of the day

Imagining all that, is it even worth trying to achieve even a moderate level of test coverage? Or should you, in this imaginary scenario, just keep doing the best you can with what you've been given and hoping, praying, maybe even sacrificing, that the client will agree to a rewrite one of these days and THEN you can start writing tests?ADDENDUMSince many of you brought it up: I have approached the possibility of a re-write at every chance I've had to date. The marketing people I work with know that their code is crap, and they know it's the fault of the "lowest bid" firm they went with originally. I've probably overstepped my bounds as a contractor by pointing out that they spend a crap ton of money on me to provide hospice care for this site, and that by redeveloping it from scratch they would see an ROI very quickly. I've also said that I refuse to rewrite the site as-is, because it doesn't really do what they want it to do anyway. The plan is to rewrite it BDD style, but getting all the key players in one place is tough, and I'm still not sure they know what they need. In any case, I fully expect that to be A Very Big Project.Thanks for all the feedback so far!