#Fake Inject

A Fake Function Inject Assistant for C

Fake inject is a assistant tool for the fake function replacement during unit test. So that it can be easier to replace the dependancy with test double.

Hello, fake inject!

Say you have such production code.

//dice.c
#include <stdio.h>
#include "dice.h"
#include <stdlib.h>

int dice_point()
{
	srand(time(NULL));
	int r = ( rand() % 6 ) + 1;
	return r;
}

int isWon()
{
	int points = dice_point();
	if (points > 3){
		return TRUE;
	}
	return FALSE;
}

If you would like to test the function isWon(), but it depends on the function dice_point() which will generate the random number, it's hard to be tested. There is a way to write a fake function of dice_point() which is called dice_point_fake()

static int closed_share_point(bool write, int value)
{
    static int saved_value;
    if (write) return saved_value;
    return saved_value = value;
}

void set_points(int points)
{
    closed_share_point(false, points);
}

int dice_point_fake()
{
    return closed_share_pont(true, 0);
}

So basic replace the dice_point with dice_point_fake is:

...
#include "fake_inject.h"
...
TEST(DiceTest, GivenDiceWhenPointBiggerThanThreeShallWin)
{
	set_points(3 + 1);
	SET_FAKE_INJECT(dice_point, dice_point_fake);
	CHECK_EQUAL(1, isWon());
	RESET_FAKE_INJECT(dice_point);
}

Cheat Sheet

Macro	Description	Example
SET_FAKE_INJECT(function_name, fake_name);	Use fake function replace original function.	SET_FAKE_INJECT(dice_point, dice_point_fake);
RESET_FAKE_INJECT(function_name);	Reset the fake function to original real function.	RESET_FAKE_INJECT(dice_point);