What's the least testable code you've had the pleasure of dealing with?
From my first commercial software job: a few thousand lines of complex C++ (mix of decoding the output of a mathematical model mixed with business rules) structured as a single "god class" with heaps of internal state and a dozen methods -- comically all of the methods would return void and took no arguments, and would call each other. It took days of careful refactoring and consultations with a colleague until it was possible to instantiate one of the things in a test harness and do nothing with it. In some sense this was dead simple code as there were no dependencies on external resources or concurrency.
From my first commercial software job: a few thousand lines of complex C++ (mix of decoding the output of a mathematical model mixed with business rules) structured as a single "god class" with heaps of internal state and a dozen methods -- comically all of the methods would return void and took no arguments, and would call each other. It took days of careful refactoring and consultations with a colleague until it was possible to instantiate one of the things in a test harness and do nothing with it. In some sense this was dead simple code as there were no dependencies on external resources or concurrency.