Why should I use asserts?

Question

I never got the idea of asserts -- why should you ever use them?

I mean, let\'s say I were a formula driver and all the asserts were things like security belt, helm

Answer 1

Just don't use Assertions when you don't want. There is nothing wrong not to use it.

Assertion is only helpful when a test case in debug mode actually hit it. Many times it doesn't hit at all, depends on quality of your test cases. Assertion is used when you try to verify an assumption, so you got what you asked for, you hardly break your assumption during test. That's why you assume it in first place isn't it. Yet there are endless number of "expected impossible" cases that really don't hit your assertion during debug, but somehow still hit in production which have assertion disabled. If you rely on assertion during debug then you most likely end up having some unexpected thing happen in production that even your assertion didn't catch.

Your program should be designed in a strategic way, so that even unexpected matter happen or your test cases didn't cover, a problem is still handled in a defined way, or produce meaningful diagnostic info.

You can use assertion to help troubleshooting, but it is not helpful if you want to prevent problem from happening in first place. The reason is that you can't prevent or handle a niche problem if you assume it won't happen in production (you disable assertion in Production). Good software should catch obvious errors (assertion helps), as well as niche errors (assertion probably won't help).

Many people will tell you a standard version of what is assertion supposed to do. What assertion is good for etc. But please justify by your own experience if it is really helpful or not. Assertion is not scientific proven or golden rule, it is just a practice of many people. You should decide to adopt it or not by yourself.

Answer 2

I've written code where the assertions demonstrably affected performance when enabled. Checking the pre- and post-conditions of maths functions used in tight loops by your graphics code, for example (square root function squares its result and compares it against the input, etc). Sure, it's on the order of a few percentage points, but I've written code that needed those few points.

More importantly, I've written code where the assertions made a tens-of-percentage-points difference to the size of the code. When memory footprint is an issue, asserts in release code are probably an unacceptable extravagance.

Answer 3

From Code Complete 2: "Use error-handling for conditions you expect to occur; use assertions for conditions that should never occur."

A commonly-cited example is checking for zero in the denominator before a division.

You're expected to strip the assertions out of production code. They are in there during development to help you catch mistakes.

Unit tests are not a replacement for assertions.

Answer 4

They enable you to test your assumptions. For example, let's say that you wanted to calculate speed. You would probably want to assert that your calculation is less than the speed of light.

Assertions are for development, to make sure you don't mess up.

Answer 5

From your post, it sounds like you are not disagreeing with the idea of using assertions, but rather the idea of having assertions in debug and not having them active in production.

The reason for this is that when debugging, you might want the process to fail catastrophically -- i.e. throw an exception and quit, so that the error can be addressed. In production, this could affect your entire system, and the error condition could occur only for a very few cases. So, in production you would probably want to log the error, but keep the process running.

Using assertions lets you change the behavior between debug and release.

I agree with you that the assertions should not just be silenced in production code -- many errors are not exposed in test environments and it is important to know when assertions fail in production.

Answer 6

For other answers to this question

assert() macro is used to test the conditions or assumptions that should not occur in a program. For example, the array index should always be > 0. Another assumption can be 2+2 == 3+1.

So using assert () we can test such assumptions and as long as they evaluate to true, our program runs normally. When they are false, the program is terminated.

more here https://www.softwaretestinghelp.com/assert-in-cpp/