I worked at Orbitz which has a huge Java codebase. It was complex and hard to maintain. It was loaded with abstractions, interfaces and unit tests. I believe the former was mostly due to the latter.

Not to say that the latter has no merits -- there are situations and cases where they are 'net win' good things. But when overdone or done poorly they make a codebase much harder to understand, troubleshoot, extend or fix.

I've seen this first-hand many times, though I notice it most often occurs in large corporate Java shops rather than with smaller companies or codebases or more nimble/concise languages.