googlemock how to use mocking in test - c++

Question

I'm a beginner with google mock and I'm not sure how to use it and the concept.
If I'm trying to Test a method from a class that is calling some other methods from different classes.
Do I need to mock all these methods from this different classes that my Test method is calling.
Here is a example:
class A {
public:
A () {}
int setnum(int num) {//do some stuff return 1 or 0//
}
private:
int _num;
};
class B {
public:
B (){}
int init(A *a, int number){
if(a->setnum(number))
return 1;
return 0;
}
void setNum(int num){_num=num;}
private:
A *_a;
int _num;
};
class C {
public:
int doSoemthing(A *a, int number){
if (domore(a,number))
return 1;
return 0;
}
int domore(A *a, int number){
if(_b.init(a,number))
return 1;
return 0;
;}
private:
B _b;
};
Do I need to mock all the methods from class A and B that I need to Test my Test method?
Or can I just mock one Class , and test if this class is working.

Answer 1

In order to test C class with mocks, you need to introduce an interface for the dependency than is to be used in C class (here, added BIface). Then you need to use dependency injection of BIface to C class (via added ctor). Having that you will be able to test interactions of B and C classes. IMO A class doesn't need to be mocked in CTest (but most probably need to be tested in BTest)
class A {
public:
A() {} // not needed
int setnum(int num) { // do some stuff return 1 or 0//
}
private:
int _num;
};
class BIface {
public:
virtual ~BIface() = default;
virtual int init(A *a, int number) = 0;
virtual void setNum(int num) = 0;
};
class B : public BIface {
public:
B() {} // not needed
int init(A *a, int number) override {
if (a->setnum(number))
return 1;
return 0;
}
void setNum(int num) override {
_num = num;
}
private:
A *_a;
int _num;
};
class C {
public:
C(BIface &b) : _b{b} {}
int doSoemthing(A *a, int number) {
if (domore(a, number))
return 1;
return 0;
}
int domore(A *a, int number) {
if (_b.init(a, number))
return 1;
return 0;
;
}
private:
BIface &_b;
};
class BIfaceMock : public BIface {
public:
MOCK_METHOD2(init, int(A *, int));
MOCK_METHOD1(setNum, void(int));
};
TEST(CTest, givenDoingMoreWhenInitOfBReturnOneThenReturnOne) {
// can be done in CTest ctor if more tests are needed to avoid code duplciation
BIfaceMock bMock{};
A a{}; // `a` doesn't need to be mocked in CTest. It shall be mocked in BTest as it is dependency of B class, not C class
C testedObject{bMock}; // dependency injection of BFace to C
const auto SOME_INT_PARAM = 42;
// Eq mather is used to match both &a and SOME_INT_PARAM. This confirms proper parameters were passed to init
EXPECT_CALL(bMock, init(&a, SOME_INT_PARAM)).WillOnce(Return(1));
ASSERT_EQ(1, testedObject.domore(&a, SOME_INT_PARAM));
}

Answer 2

I'm not 100% sure but in your example you don't have to use mocks at all. You can create your objects really easy here.
I would use mocks when I would expect that some method will be called and should return specific value - I'm not testing this method but for example if-statment:
A a;
if(a.method())
{
// some logic
}
To manipulate what if will get I would use mocks like this: EXPECT_CALL(aMock.method()).WillOnce(Return(true));
But you can use it in many more situations (e.g: you can avoid creating really big class and replace it with mock object).