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Comment by mickeyben | Hacker News Reader

How would you write unit tests to test against services not responding and routing issues between your different instances ?

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That's what mock objects are for. You mock the object that would normally call the remote system, have it artificially fail, and use that to test clients of that object.

So you only test those cases you have thought can fail(which is compulsory to test anyway). The purpose of the Monkey Chaos is to trigger situations you haven't dreamed about.

OK, it ain't perfect. Things usually doesn't fail in a uniformaly distributed way and you can't be sure you'll see a different kind of fail on production, but it sounds useful(yeah, and pretty cool) nonetheless.

Why are people replying to me as if I ever said that Chaos Monkey was a bad idea? I was responding to a question about how to unit test remote system failures. Obviously that's not the only testing you're going to do.

The problem is "artificially fail". You need to ensure that the systems work in production even after real failures.

SQLite [1] uses a test harness to do this:

"SQLite responds gracefully to memory allocation failures and disk I/O errors. Transactions are ACID even if interrupted by system crashes or power failures. All of this is verified by the automated tests using special test harnesses which simulate system failures. "

http://www.sqlite.org/about.html

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