Google测试中的存根系统功能 [英] Stub system function in google test

问题描述

我正在尝试使用Google Test测试C代码，但遇到一些与系统功能的写存根相关的问题，例如:fopen，fclose，fread，fwrite，memcpy，memset，stat等...知道如何正确地对它们进行存根以覆盖功能中需要测试的所有分支.

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.

示例，我有一个函数，如何通过存根fopen，fclose，fwrite，fread对其进行测试?只有存根，没有模拟.

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;
}

推荐答案

sample.c 中的 file()函数调用 fopen().在完全不同的文件(编译单元)中将 fopen 定义为其他内容不会改变这一点.

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.

您不能简单地模拟一个免费功能.

您可以更改 file()函数以获取指向要使用的 fopen()函数的指针.然后，在测试中，当调用 file()函数时，您将提供一个指向模拟函数的指针.这是依赖注入的一种形式.

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.

另一种选择是使用条件编译.

Another option is to use conditional compilation.

使用依赖注入的示例:

// 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`.
}

然后在您的测试代码中:

And then in your test code:

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

如果使用许多要模拟的系统功能，则还可以创建一个结构，其中包含指向所有相关功能的指针.

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;
}

这里的前提是，如果要测试代码，则需要编写可测试的代码.依赖注入是实现此目标的一种方法.

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.

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