If as assert fails, is there a bug?

Question

I've always followed the logic: if assert fails, then there is a bug. Root cause could either be:

• Assert itself is invalid (bug)
• There is a programming error (bug)
• (no other options)

I.E. Are there any other conclusions one could come to? Are there cases where an assert would fail and there is no bug?

Answer 1

If assert fails there is a bug in either the caller or callee. Why else would there be an assertion?

Answer 2

Yes, there is a bug in the code.

Code Complete

Assertions check for conditions that should never occur. [...]

If an assertion is fired for an anomalous condition, the corrective action is not merely to handle an error gracefully- the corrective action is to change the program's source code, recompile, and release a new version of the software.

A good way to think of assertions is as executable documentation - you can't rely on them to make the code work, but they can document assumptions more actively than program-language comments can.

Answer 3

That's a good question.

My feeling is, if the assert fails due to your code, then it is a bug. The assertion is an expected behaviour/result of your code, so an assertion failure will be a failure of your code.

Answer 4

Only if the assert was meant to show a warning condition - in which case a special class of assert should have been used.

So, any assert should show a bug as you suggest.