Can gmock be used for stubbing C functions?

Question

I am new to gmock, so I want to know how can I stub simple C function called in a function under test for Unit Testing.

Example:

int func(int a)
{
           


        

Answer 1

I was looking already a long time for a solution to mock legacy c-functions with googleMock without changing existing code and last days I found the following really great article: https://www.codeproject.com/articles/1040972/using-googletest-and-googlemock-frameworks-for-emb

Today I wrote my first unit test for c-functions using gmock and took as example two functions from the bcm2835.c library (http://www.airspayce.com/mikem/bcm2835/) for raspberry Pi programming: Here is my solution: I'm using the gcc 4.8.3. under Eclipse and Windows. Be Aware to set the Compiler option -std=gnu++11.

Here are my functions to be tested

int inits(void);
void pinMode(uint8_t pin, uint8_t mode);

int inits(){
    return bcm2835_init();
}

void pinMode(uint8_t pin, uint8_t mode){
    bcm2835_gpio_fsel(pin, mode);
}

Includes and defines for unit testing with googleTest / googleMock

// MOCKING C-Functions with GMOCK :)
#include 
#include "gtest/gtest.h"
#include "gmock/gmock.h"
using namespace ::testing;
using ::testing::Return;

Mock BCM2835Lib functions

class BCM2835Lib_MOCK{
public:
    virtual ~BCM2835Lib_MOCK(){}

    // mock methods
    MOCK_METHOD0(bcm2835_init,int());
    MOCK_METHOD2(bcm2835_gpio_fsel,void(uint8_t,uint8_t));
};

Create a TestFixture

class TestFixture: public ::testing::Test{
public:
    TestFixture(){
        _bcm2835libMock.reset(new ::testing::NiceMock());
    }
    ~TestFixture(){
        _bcm2835libMock.reset();
    }
    virtual void SetUp(){}
    virtual void TearDown(){}

    // pointer for accessing mocked library
    static std::unique_ptr _bcm2835libMock;
};

Instantiate mocked lib functions

// instantiate mocked lib
std::unique_ptr TestFixture::_bcm2835libMock;

Fake lib functions to connect Mocks with the c-functions

// fake lib functions
int  bcm2835_init(){return TestFixture::_bcm2835libMock->bcm2835_init();}
void bcm2835_gpio_fsel(uint8_t pin, uint8_t mode){TestFixture::_bcm2835libMock->bcm2835_gpio_fsel(pin,mode);}

Create unit testing class for BCM2835 from TestFixture

// create unit testing class for BCM2835 from TestFixture
class BCM2835LibUnitTest : public TestFixture{
public:
    BCM2835LibUnitTest(){
        // here you can put some initializations
    }
};

Write the Tests using googleTest and googleMock

TEST_F(BCM2835LibUnitTest,inits){
    EXPECT_CALL(*_bcm2835libMock,bcm2835_init()).Times(1).WillOnce(Return(1));

    EXPECT_EQ(1,inits()) << "init must return 1";
}

TEST_F(BCM2835LibUnitTest,pinModeTest){

    EXPECT_CALL(*_bcm2835libMock,bcm2835_gpio_fsel( (uint8_t)RPI_V2_GPIO_P1_18
                                                   ,(uint8_t)BCM2835_GPIO_FSEL_OUTP
                                                  )
               )
               .Times(1)
               ;

    pinMode((uint8_t)RPI_V2_GPIO_P1_18,(uint8_t)BCM2835_GPIO_FSEL_OUTP);
}

Results :)

[----------] 2 tests from BCM2835LibUnitTest
[ RUN      ] BCM2835LibUnitTest.inits
[       OK ] BCM2835LibUnitTest.inits (0 ms)
[ RUN      ] BCM2835LibUnitTest.pinModeTest
[       OK ] BCM2835LibUnitTest.pinModeTest (0 ms)
[----------] 2 tests from BCM2835LibUnitTest (0 ms total)

Hope it will help :) - for me this is a really working solution.