My GUESS was that he/she means that the code has asserts in it that check if something is not right at runtime. I personally would not call that a replacement/alternative for unit tests. In fact, it may be counterproductive ... a small error in the code would bring down and entire application.
i would counter this by saying that a small error in code SHOULD bring down the entire application.... during development. otherwise the error is not visible to developers when they can best/easiest fix it.
of course, asserts should not crash the app once it's in production. instead they should be channeled to a log that gets sent back to the production support team for analysis.
but during development, I'd say crashing during small errors is a great thing.
