How write a unit test for verifying compiling error?

Question

I'm trying to write a test to verify a compiling error. It's about assigning a number to a String type property. But since it's a compiling error, the unit test code won't even be compiled at the first place. So anyone have any suggestion on how to do this?

I'm thinking maybe I can assign the number in runtime and check to see if certain exception got thrown? But I'm not sure how exactly to do that.

Thanks in advance!

You could generate a peace of code that you know should and one that should not compile and feed that to your compiler (through command line) and check the results in your unit test. However, I typically agree with icyrock.com's answer. — Steven, Nov 21 '10 at 12:12
To be able to do this while staying in the same testing environment you would probably need some try-catch feature on compiler level. Would actually be a very nice feature to have. Or easier, some compiler-annotation like `@skip-on-compile-error` above a class/struct/function/block. — DarkTrick, Jan 08 '23 at 03:22

icyrock.com · Accepted Answer · 2010-11-21T15:30:15.550

If I understand you correctly, you have some piece of code that may not compile and you want to write the unit test that fails if the code really doesn't compile. If that is the case, then you should not write any unit tests. You should understand that you should write unit tests only for your code, not the code that somebody else wrote.

You didn't specify the programming language, so I will do some pseudo-code. Say you are writing a function to add two numbers:

function add(a, b) {
   return a + b;
}

Very simple. You should unit test this, e.g. by making tests like the below:

function testAdd() {
   assertEquals(4, add(2, 2));
   assertEquals(46, add(12, 34));
}

However, you should not write a test that tests whether + operator is working fine. This is the job of whoever wrote the library that implements how + operator really works.

So, if that's the case, don't write any unit tests. Compiling your code is job of your compiler. The compiler should report that there is a compilation error in a proper way. You should not test whether compiler does its job correctly - testing that is the job of the people who are writing the compiler.

(1) "You should not test whether compiler does its job correctly" language specs can contain implementation-defined-details, and if you leverage on such details -- it will be cool to check it (2) You can intoduce some compile time mechanisms in your project -- and potentionally you can want to check it) — Konstantin Burlachenko, Aug 02 '15 at 01:03
p.s. @icyrock.com, you have a very-very-very big level with 15.5K) So I really think that you know all about it) — Konstantin Burlachenko, Aug 02 '15 at 01:07

score 1 · Answer 2 · edited Jan 30 '21 at 06:16

You did not specify the language

Ruby, Python -- dynamic & strong typesystem. This means that the types deduced during runtime (dynamic), but implicit conversions between types are prohibited
Js, Perl -- dynamic & weak typesystem.
C++ -- static and strong typesystem.

Let's assume we are talking about C++. Moreover I can create more really example. Imagine that you implement static assert for your project which doesn't not use c++11 compiler

template <bool>
struct my_static_assert;

template <>
struct my_static_assert<true> {};

If you want to check that such mechanism works ok. You should create unittest function which do the follow steps:

Create some file to compiler
Create external process of the compiler and pass test compile unit to it
Wait for compiler process completion
Retrive return code from the compiler process
Your function check return code from 4.

I checked google-test guide but it seems that they doesn't support such concept https://github.com/google/googletest/blob/master/docs/advanced.md

How write a unit test for verifying compiling error?

2 Answers2

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