c++ - How do I use GMock with dependency injection? -

i have class carries couple of dependencies i'd mock using google mocks, in order test class google test.

simplified, have following¹:

template<typename tdep> class sut { private:     tdep dependency;  public:     explicit sut(const tdep& dep) : dependency(dep) { }     sut(const sut& other) : dependency(dep.other) { }      // methods use dependency } 

i have interface dependency,

class idependency { public:     virtual double calculatecoolstuff(double) const = 0;     virtual ~idependency() { }; } 

and mock object

class mockdependency { public:     mock_const_method1(calculatecoolstuff, double(double)); }; 

however, when try compile like

mockdependency mock; sut sut(mock); 

i errors stating error: use of deleted function mockdependency(const mockdependency&), i.e. there no copy-constructor of mocked object. found this discussion on google groups ends in making mock objects non-copyable, allowing user add copy constructor , define copy behavior manually. well:

class mockdependency { public:     mockdependency(const mockdependency& other) { }     mock_const_method1(calculatecoolstuff, double(double)); }; 

now code compiles, if run like

mockdependency mock; sut sut(mock);  expect_call(mock, calculatecoolstuff(2.0)).willrepeatedly(return(3.0));  sut.dostuff(); // calls calculatecoolstuff 

in test, error stating call never set up. in other words, instance mock can use setup expectations, no longer same instance on sut used calculations. makes testing gmock , di difficult, least...

what best solution this?

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^{1) yes, i'm using poor man's di. not topic of conversation...}

you can use dependency injection references ensuring class member reference:

template<typename tdep> class sut { private:     tdep& dependency;  // reference      // etc. } 

note no longer need copy constructor on mockdependency. rule, need access instances of mock objects being used sut set expectations on them.