Using gmock in C code

[kumar]

Hi,

I am trying to see if it is possible to use gmock on functions written in pure C. I do not want to "mock" the functions really, but be able to assert on the number of times it was called, with what parameters, etc.

Example: [production_code.c]

void outer(void)

{

     inner(1234);

}

I'm calling ``outer()`` from my test case and want to know whether inner( ) was called once, with the value 1234. How to do this? Note that I really want the call to inner() to happen, not just mock it out by an empty implementation.

I looked at the sections "Mocking Free Functions" and "Delegating Calls to a Real Object" in the Cookbook, but both of them assume that the production code is written in C++, not C. I can only write my test code in C++, not production code. What are my options?

Thanks!

[Keith Ray]

It would work better if you use CMock or another C-language-based mocking tool. In order to stub or mock a C function, you have to have your test link against a different implementation of that C function. (Or use function pointers.)

https://github.com/ThrowTheSwitch/CMock/blob/master/docs/CMock_Summary.md

One way of using function-pointers is something like this (pseudo C/C++ code):

Instead of this in the header:

void inner(int x);

use this:

typedef void (*InnerFunc)(int x);

extern InnerFunc inner;

In the implementation of inner:

static void inner_impl(int x) { 

... etc..... 

}

InnerFunc inner = inner_impl;

In the test:

static void inner_mock(int x) { 

... etc..... 

}

...blah blah gmock test stuff....

setup() {

save_inner = inner;

inner = inner_mock;

}

teardown()

{

inner = save_inner;

}

test()

{

set expectations for inner_impl

outer();

assert that expectations for inner_impl were satisfied

}

Syntax of the production code remains the same (though now it is actually calling a function-pointer instead of direct reference to the function.)

void outer(void)
{
      inner(1234);
}

This book explains how you can do TDD and mocking in C:

Test Driven Development for Embedded C (Pragmatic Programmers)

--
C. Keith Ray
* (650) 539-4729

* https://www.dropbox.com/s/mpoefyt9bz1yoxx/keith_ray_resume.pdf

* http://agilesolutionspace.blogspot.com/

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