Google mock global mock object memory leak

Question

I am using VS2005, and C++ for unit testing using google mock.
I had a global free function in unit testing, and I used the following code to mock free function:

NiceMock <MockA> mockObj;  



struct IFoo {  
    virtual A* foo() = 0;  
    virtual ~IFoo() {}  
};  

struct FooMock : public IFoo {  
    FooMock() {}  
    virtual ~FooMock() {}  
    MOCK_METHOD0(foo, A*());  
};

FooMock fooMock;

// foo() implementation  
A* foo() {  
    return fooMock.foo();  
}

In the SetUp() function, I set Expectations on the global object like

EXPECT_CALL(fooMock,foo())  
    .Times(1)  
    .WillOnce(Return(&mockObj));  

TEST(..., instA) {

    // ...
}

and in TearDown(), I delete the global mock object fooMock

virtual TearDown(){  
    delete &fooMock;  
}

When I run the code, I get the following error

Error: Memory Leak in xyz.instA,

also,
0 bytes in 0 Free Blocks.
-61 bytes in -1 Normal Blocks.
68 bytes in 7 CRT Blocks.
0 bytes in 0 Ignore Blocks.
0 bytes in 0 Client Blocks.
Largest number used: 11025 byte
Total allocations: 50602 bytes.

Can anyone tell me what is happening here? If I don't delete fooMock, I get the error "fooMock should be delete but never is", or Heap corruption detected.
From the error, I can see that somewhere my heap is being mishandled, but I cannot find the point. I have tried to debug it step by step as well.

Some help would be really great! :)

You must not delete `fooMock` because it does not have dynamic storage. `fooMock should be delete but never is` or `Heap corruption detected` are either not reported due to the shown code (minus the delete) or the error reporter is buggy. — eerorika, Feb 12 '15 at 11:20
@user2079303: I removed the delete statment, now I have this error: ..\xyzTest.cpp(73): ERROR: this mock object (used in test xyzTest.instA) should be deleted but never is. Its address is "0053DFA0." ERROR: 1 leaked mock object found at program exit. and line 73 points in SetUp() method at this code: EXPECT_CALL(fooMock,foo()) .Times(1) .WillOnce(Return(&mockObj)); — Muhammad Hassan, Feb 12 '15 at 11:31
Hmm, I'm not familiar with googlemock. Perhaps it requires the mock object to be allocated dynamically? — eerorika, Feb 12 '15 at 11:56
That depends on the scenario. But I have already tried that, gives the same error as in my original post. Maybe I am doing something wrong during mocking. — Muhammad Hassan, Feb 12 '15 at 11:57
possible duplicate of [how to mock global free function using gmock](http://stackoverflow.com/questions/28668892/how-to-mock-global-free-function-using-gmock) — Ian, Feb 23 '15 at 15:35

score 3 · Answer 1 · edited Feb 07 '23 at 16:17

As Ian stated:

Googlemock/googletest expect the mock to be defined either within the body of the test, or within a test fixture class.

The idea behind it is explained in the Cookbook:

When it's being destroyed, your friendly mock object will automatically verify that all expectations on it have been satisfied, and will generate Google Test failures if not. This is convenient as it leaves you with one less thing to worry about. That is, unless you are not sure if your mock object will be destroyed.

In your case fooMock is a global variable (and as you stated it must stay this way) so after each test you just need to run manual verification:

    using ::testing::Mock;

    TEST(..., instA) 
    {
       ASSERT_TRUE(
           Mock::VerifyAndClearExpectations(
            &fooMock));
    }

Since it is a global variable you can also just do:

Mock::AllowLeak(&fooMock);

More details in Cookbook - Forcing a Verification and CheatSheet - Verifying and Resetting a Mock:

score 2 · Answer 2 · answered Feb 13 '15 at 20:20

2

It looks like the problem is that you're instantiating a global instance of FooMock. Googlemock/googletest expect the mock to be defined either within the body of the test, or within a test fixture class.

In the example above, you'd simply instantiate fooMock inside the test:

TEST(..., instA) {

    FooMock fooMock;
    // ...
}

answered Feb 13 '15 at 20:20

Ian

842
5
16

If I add it inside the Test case, I won't be able to access it in global function. Same applies to test fixture class. – Muhammad Hassan Feb 13 '15 at 20:22
Can you provide some additional detail about why you need the global function? Why not either (1) define foo() as a member function of a test fixture class, or (2) pass the FooMock as a parameter to foo()? – Ian Feb 16 '15 at 21:42
Well, since i have foo() as a global function in my sources, i couldn't find a way to mock it, and i didn't want to change the sources like creating an interface as mentioned in google cookbook. So, i asked here how i can mock the scenario and someone gave this solution. It worked but I'm facing memory leaks now. So, maybe we are still missing something. – Muhammad Hassan Feb 17 '15 at 10:02
Ah, okay. It wasn't clear that the goal here was to mock a global function. I'm not aware of a mechanism for doing what you want; the approach that you've outlined above doesn't work because it violates the lifetime semantics of mock objects. If you _do_ find a way to make this work, please let me know, because I'd love to see it :) – Ian Feb 17 '15 at 21:36
Oops, I didn't know that i cannot use a global mock object. I will update the answer here when I find one. – Muhammad Hassan Feb 18 '15 at 06:20
I read somewhere that we can use global mock objects. But anyway, so far I haven't been able to solve it. Will post a query again. – Muhammad Hassan Feb 23 '15 at 07:18

Zeeshan Abid · Answer 3 · 2019-09-12T00:25:50.927

So I stumbled upon this question and couldn't figure out a way. But then being a software engineer, I needed to find a solution. So here is what I did.

Suppose you want to mock a Queue. The one function you want to mock is dequeue. I will assume you want to dequeue integers to keep things simple because I want to demonstrate how to make global mocks without memory leaks.

class QueueInterface {
    public:
        virtual ~QueueInterface() {};
        virtual int dequeue() = 0;
};

class QueueMock : public QueueInterface {
    public:
        virtual ~QueueMock() {};
        MOCK_METHOD(int, dequeue, (), (override));
};

// Instead of a global object, have a global pointer
QueueMock *globalQueue;

class TestFixture : public ::testing::Test {
    protected:
        QueueMock mockedQueue;

        void SetUp() {
            globalQueue = &mockedQueue; // Point the global pointer to this queue
        }

        void TearDown() {
            globalQueue = NULL;
        }
}

// Now you can use this global queue pointer in free function or
// C style functions and override the existing implementations.
// This way you can mock a global object.

int dequeueFromQueue() {
   return globalQueue->dequeue();
}

TEST_F(TestFixture, DEQUEUE_TEST) {
    // Write your test here to use global queue pointer
    // Deref pointer to get mocked object
    EXPECT_CALL(*globalQueue, dequeue);
}

In this way, whenever a new test is executed, the member variable mockedQueue is allocated and then deallocated at the end of the test. The globalQueue would point to the member instance of each test every time.

Hope this helps! :)

score 1 · Answer 4 · answered May 10 '21 at 03:10

I ran into the same problem and here is the solution (not sure what exactly happened inside because the global mock obj will be destructed eventually).

std::unique_ptr ptrMockObj(new FooMock ());

At the end of the test case, delete the mock obj ptr

TEST(..., instA) { ... ptrMock.Obj.reset() }

Google mock global mock object memory leak

4 Answers4

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