C++: How to unit test a scoped_ptr?

Question

Suppose I have implemented a scoped_ptr:

template <typename T> class scoped_ptr {
 public:
  scoped_ptr() = delete;
  explicit scoped_ptr(T *ptr) : _ptr(ptr){};
  ~scoped_ptr() {
    delete _ptr;
    _ptr = nullptr;
  };

  scoped_ptr(const scoped_ptr &p) = delete;
  scoped_ptr &operator=(const scoped_ptr &p) = delete;

  T *operator->() const { return _ptr; }
  T &operator*() const { return *_ptr; }
  T *get() const { return _ptr; }
  void reset(T *p = nullptr) {
    delete _ptr;
    _ptr = p;
  }

 private:
  T *_ptr;
};

I want to test that the memory is actually freed after the pointer's lifetime is over, but I cannot verify this by dereferencing that raw pointer _ptr because it is expected that the memory it pointed to should have already been released. Then how do I test it?

You could test it with a specially designed class that does something testable in its destructor and/or `operator delete` — Igor Tandetnik, Apr 14 '19 at 14:56

score 1 · Accepted Answer · answered Apr 15 '19 at 06:31

How about using a class with object counts? Side note: you need to check for self-assignment in reset.

Demo: https://ideone.com/hnxc9o.

#include <cassert>
#include <iostream>

using namespace std;

template <typename T>
class scoped_ptr {
 public:
  scoped_ptr() = delete;
  explicit scoped_ptr(T *ptr) : _ptr(ptr) {}
  virtual ~scoped_ptr() { reset(); }

  scoped_ptr(const scoped_ptr &p) = delete;
  scoped_ptr &operator=(const scoped_ptr &p) = delete;

  T* operator->() const { return _ptr; }
  T& operator*() const { return *_ptr; }
  T* get() const { return _ptr; }
  void reset(T* p = nullptr) {
    if (_ptr == p) {
      return;
    }
    delete _ptr;
    _ptr = p;
  }

 private:
  T* _ptr;
};

struct ObjectCounter {
  static int _object_count;
  ObjectCounter() {
    ++_object_count;
  }
  virtual ~ObjectCounter() {
    --_object_count;
  }
};

int ObjectCounter::_object_count = 0;

int main() {
  {
    scoped_ptr<ObjectCounter> ptr(new ObjectCounter());
    assert(ObjectCounter::_object_count == 1);
  }
  assert(ObjectCounter::_object_count == 0);
  return 0;
}

C++: How to unit test a scoped_ptr?

1 Answers1