Where to begin.. perhaps the projects with code metrics tied into the check in system - want to commit code changes? You're now on the hook to provide at least 85% unit test coverage or the source control tool will not accept it. So what did most people do? They wrote useless tests, assert true equals true, no-ops or pass statements, basically anything to just get past the arbitrary metric.
Or how about another project that had lots of real tests, that were old, unmaintained, did humongous amounts of work in each single unit test and took a weekend to run, and of course, fail.
Or perhaps the team that obsessed about the testing for each user story, spent all the time doing that, then running out of time to deliver the actual stories.
And those were the less egregious examples!