Stub system function in google test

问题

I am trying to use Google Test to test C code but I am encounter some problem related to write stub for system functions like: fopen,fclose,fread,fwrite, memcpy,memset,stat,...I don't known how to stub them correctly to cover all branchs in function that need to be tested.

Example , I have a function, how to test it by stub fopen, fclose, fwrite, fread? Only Stub, not Mock.

#include <stdio.h>
#include <stdlib.h>

int main(){
    FILE *f;
    //initialize the arr1 with values
    int arr1[5]={1,2,3,4,5};
    int arr2[5];
    int i=0;

    //open the file for write operation
    if((f=fopen("includehelp.txt","w"))==NULL){
        //if the file does not exist print the string
        printf("Cannot open the file...");
        exit(1);
    }
    //write the values on the file
    if((fwrite(arr1,sizeof(int),5,f))!=5){
        printf("File write error....\n");
    }
    //close the file
    fclose(f);

    //open the file for read operation
    if((f=fopen("includehelp.txt","r"))==NULL){
        //if the file does not exist print the string
        printf("Cannot open the file...");
        exit(1);
    }
    //read the values from the file and store it into the array
    if((fread(arr2,sizeof(int),5,f))!=5){
        printf("File write error....\n");
    }
    fclose(f);

    printf("The array content is-\n");
    for(i=0;i<5;i++){
        printf("%d\n",arr2[i]);
    }

    return 0;
}

回答1:

Your file() function in sample.c calls fopen(). Defining fopen as something else in a totally different file (compilation unit) is not going to change that.

You cannot simply mock a free function.

You can change the file() function to take a pointer to the fopen() function to use. In your tests you then provide a pointer to your mock function when calling the file() function. This is a form of dependency injection.

Another option is to use conditional compilation.

An example of using dependency injection:

// Typedef for our "fopen interface". Makes our code a bit more readable.
typedef FILE *(*fopen_type)(const char *, const char *);

FILE *file(fopen_type fopen_func)
{
    FILE *f = fopen_func("abc", "r"); // Call the provided "fopen" function.
    return f; // Let's return the opened file or `NULL`.
}

And then in your test code:

TEST(OPEN_FILE, OK)
{
    ASSERT_NE(NULL, file(&my_fopen));
}

If you use many system functions that you want to mock, you can also create a struct that contains pointers to all the relevant functions.

struct system_calls {
   fopen_type fopen;
   // Add more system calls here.
};

FILE *file(struct system_calls *p)
{
    FILE *f = p->fopen("abc", "r");
    return f;
}

The premise here is that if you want to test your code, you need to write testable code. Dependency injection is one way to achieve that.

来源：https://stackoverflow.com/questions/59394613/stub-system-function-in-google-test

标签

unit-testing

googletest