FFF fake function with google test

I am trying to test my C library with google test but I'm having trouble mocking functions with the fff.h framework. This is my file structure:

.
├── Makefile.am
├── configure.ac
├── include
│   ├── Makefile.am
│   └── public_header.h
├── src
│   └── libmylib
│       ├── Makefile.am
│       ├── private_functions.c
│       ├── private_functions.h
│       ├── libmylib.la
│       └── libmylib.c
└── test
    └── libmylib_test
        ├── Makefile.am
        ├── fff.h
        └── test.cc

I want to mock a function from the header private_functions.h which is used in a function from the public_header.h using the fff.h framework.

public_function()
{
        private_function(); //This function is the one I want to mock.
}

My test looks like this:

#include "gtest/gtest.h"
#include "public_header.h"
#include "fff.h"

extern "C" {
    #include "private_functions.h"
}

DEFINE_FFF_GLOBALS;

FAKE_VALUE_FUNC(int, function, char *, char *);

class libtest : public testing::Test
{
public:       
    virtual void SetUp()
    {
        RESET_FAKE(function);
    }

    virtual void TearDown()
    {
    }
};

TEST_F(libtest, test_fff)
{
    public_function("val1", "val2");
    EXPECT_EQ(function_fake.call_count, 1);
}
...

When I run make it says that the private_function() is defined multiple times.

My test/libmylib_test/MakeFile.am looks like this:

LIBSRC = $(top_srcdir)/src/libstorage

check_PROGRAMS = libmylib_test
libstorage_test_SOURCES = test.cc
libstorage_test_CFLAGS = $(AM_CFLAGS)
libstorage_test_CXXFLAGS = -I$(top_srcdir)/include -I$(LIBSRC) -std=c++11 $(AM_CPPFLAGS)
libstorage_test_LDFLAGS = $(AM_LDFLAGS) -static -pthread
libstorage_test_LDADD = $(top_srcdir)/src/libmylib/libmylib.la

I have a solution but I'm not sure if it's the best one.

When I compile my library I want to test it generates .o files for every .c file I have. As I only want to test libmylib.c I linked only libmylib_la-libmylib.o instead of the .la file.

The generated .o files in src/libmylib/ were:

libmylib_la-libmylib.o
libmylib_la-private_functions.o

My updated MakeFile.am in ./test/libmylib_test/ looks like this now:

LIBSRC = $(top_srcdir)/src/libstorage

check_PROGRAMS = libmylib_test
libstorage_test_SOURCES = test.cc
libstorage_test_CFLAGS = $(AM_CFLAGS)
libstorage_test_CXXFLAGS = -I$(top_srcdir)/include -I$(LIBSRC) -std=c++11 $(AM_CPPFLAGS)
libstorage_test_LDFLAGS = $(AM_LDFLAGS) -static -pthread
libstorage_test_LDADD = $(top_srcdir)/src/libmylib/libmylib_la-libmylib.o

As I had another function in the private_functions.h I had to mock that one too because it was not defined elsewhere.

After these updates the tests compiled without problems and ran fine.

Test file now looks like this:

#include "gtest/gtest.h"
#include "public_header.h"
#include "fff.h"

extern "C" {
    #include "private_functions.h"
}

DEFINE_FFF_GLOBALS;

FAKE_VALUE_FUNC(int, function, char *, char *);
FAKE_VOID_FUNC(other_func, char *);
...