Actual function call count doesn't match EXPECT_CALL - c++

Question

Im new to Gmock. I try a example but it's error. I also refer a few posts on the group but it not helpul for me.
class MATH
{
public:
virtual ~MATH(){}
virtual int Tong(int a, int b)
{
return a + b;
}
};
class MockMATH : public MATH
{
public:
MOCK_METHOD2(Tong, int(int,int));
};
class TestMATH
{
MATH m ;
public:
int TestTong(int a, int b)
{
cout<<"TONG"<<endl;
if(m.Tong(a,b))
{
cout<<"Successful"<<endl;
return a+b;
}
else
{
cout<<"Failed"<<endl;
return -1;
}
}
};
TEST(MyMathTest, Tong_by_true)
{
MockMATH mM;
TestMATH math;
EXPECT_CALL(mM,Tong(_,_));
//.WillOnce(Return(9));
int retValue = math.TestTong(4,5);
std::cout<<retValue<<std::endl;
EXPECT_EQ(retValue,9);
}
int main(int argc, char** argv)
{
::testing::InitGoogleTest(&argc, argv);
int ret = RUN_ALL_TESTS();
return ret;
}
and this error is showed below :

Answer 1

The problem is method Tong() is never called on your mock object mM. It is called on object m, member of TestMath class. That cannot work, m is not a mock object, gmock knows nothing about it and cannot track methods being called on it.
The simplest solution I see is:
class MATH { public: virtual ~MATH(){} virtual int Tong(int a, int b) { return a + b; } };
class MockMATH : public MATH
{
public:
MOCK_METHOD2(Tong, int(int,int));
};
class TestMATH
{
MockMATH m ;
public:
int TestTong(int a, int b)
{
std::cout<<"TONG"<<std::endl;
if(m.Tong(a,b))
{
std::cout<<"Successful"<<std::endl;
return a+b;
}
else
{
std::cout<<"Failed"<<std::endl;
return -1;
}
}
MockMATH& getMMath() { return m; }
};
TEST(MyMathTest, Tong_by_true)
{
TestMATH math;
EXPECT_CALL(math.getMMath(),Tong(_,_))
.WillOnce(Return(9));
int retValue = math.TestTong(4,5);
std::cout<<retValue<<std::endl;
EXPECT_EQ(retValue,9);
}
which passes the test.