Instead of writing clean code that makes sense and is easy to reason about, he will write long-winded, poorly abstracted, weird code that is prone to breaking without an extensive "test suite" to hold the madness together and god forbid raise an alert when some unexpected file over here breaks a function over there.
Tests will be poorly written, pointless, and give an overall false sense of security to the next sap who breaths a sigh of relief when "nothing is broken". Of course, that house of cards will come down the first time something is in fact broken.
I've worked in plenty of those environments, where there was a test suite, but it couldn't be trusted. In fact, more often than not that is the case. The developers are a constant slave to it, patching it up; keeping it all lubed up. It's like the salt and pepper on a shit cake.
Testing what you do and developing ways to ensure its reliable, fault-tolerant and maintainable should be part of your ethos as a software developer.
But being pedantic about unit tests, chasing after pointless numbers and being obsessed with a certain kind of code is the hallmark of a fool.