unit testing - c++ dependency injection to test a class that class system calls -

i trying use template dependency injection test c++ class uses c system calls operate on file descriptor. ideia have abstract class , instance wrap system calls read(), write(), etc. use mock test target class. abstract class , system calls looks like: (i going omit parameters clear)

class oscall{     read()=0;     write()=0 }; class defaultoscall : public oscall{     read(){...}     write(){...} } 

later inject oscall in class want use it:

template<typename oscall> class fd{     public:         oscall oscall_;         oscall &getoscall(){return oscall_;}          read(){oscall_.read()}         write(){oscall_.write()} } 

now if want use mock test fd class need pass mock in template paramenter , mock instance using getoscall.

let's want use fd member of class:

template<typename oscall> class user{     public:         dosomething(){fd_.read();.......}         oscall &getmemberoscall(){return fd_.getoscall()}     private:         fd<oscall> fd_; } 

if want test user mock, can oscall instance using getmemberoscall, works, 1 of best ways it? in end want inject mock class member , expect return values of member's mock. hope made myself clear.

thanks

i recommend rename getmemberoscall() getoscall().

this seem enable used in conjunction generic templates template classes need implement getoscall() method, , able instantiate template either fd<oscall>, or user<oscall>. seems bit more flexible approach.