Mocking a Base class

[Neha Jain]

Hi,

I am trying to mock a base class used in my code. I havent seen any
examples and am wondering if its possible.

Element is the base class that I am trying to Mock. The class
UTManager originally inherits from Element. I have now changed it to
inherit from MockElement, since I want certain functions to be
mockable... not sure if I am doing the right thing.

My code:

class MockElement: public Element{
public:
MockElement():Element(){}

virtual ~MockElement(){}

MOCK_METHOD3(StartTimer, void(TimerId timerId, TimerDuration
timerDuration, bool bPeriodic));

};


TEST_F(TestElementMock, TEST_StartTimer)
{
MockElement* mockElement = new MockElement();

EXPECT_CALL(*mockElement, StartTimer(_,_,_))
.Times(AtLeast(1));

UTManager* pUTManager = new UTManager(); // UTManager inherits
from MockElement now
pUTManager->Initialize(); // The initialize method makes a call to
StartTimer
pUTManager->HandleTimeout(12);

delete mockElement;
}


When I run, I get the following:

[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from TestElementMock
[ RUN ] TestElementMock.TEST_StartTimer

GMOCK WARNING:
Uninteresting mock function call - returning directly.
Function call: StartTimer(12, 20, false)
Stack trace:

GMOCK WARNING:
Uninteresting mock function call - returning directly.
Function call: StartTimer(12, 20, false)
Stack trace:
TestElementMock.cpp:30: Failure
Actual function call count doesn't match EXPECT_CALL(*mockElement,
StartTimer(_,_,_))...
Expected: to be called at least twice
Actual: never called - unsatisfied and active
Test run.
[ FAILED ] TestElementMock.TEST_StartTimer (1 ms)
[----------] 1 test from TestElementMock (1 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (1 ms total)
[ PASSED ] 0 tests.
[ FAILED ] 1 test, listed below:
[ FAILED ] TestElementMock.TEST_StartTimer


Any help will be appreciated.
Thanks!
Neha

[Dean Sturtevant]

It seems you are creating 2 MockElements and setting expectations on
one, but invoking the other. Place the expectations on the object you
are using.
- Dean

[Neha Jain]

Hi Dean,

Thanks for the reply. What you are saying makes sense. But I guess I do not know how to access the mock element which is the base class of UTManager.

Maybe what I am trying to do is not possible.

Thanks

[Remco Teunen]

Hi Neha,

The problem with your particular test is that you should set the expectation on pUTManager, not mockElement. mockElement isn't used anywhere. Try this:

TEST_F(TestElementMock, TEST_StartTimer)

{

   UTManager* pUTManager = new UTManager(); // UTManager inherits from MockElement now

   EXPECT_CALL(*pUTManager, StartTimer(_,_,_))

       .Times(AtLeast(1));

   pUTManager->Initialize(); // The initialize method makes a call to StartTimer

   pUTManager->HandleTimeout(12);

   delete pUTManager;

}

However, instead of having UTManager inherit from a mock, why not just use a partial mock for UTManager itself? In other words, use the following mock:

class MockUTManager : public UTManager {

 public:

   MOCK_METHOD3(StartTimer, void(TimerId timerId, TimerDuration

      timerDuration, bool bPeriodic));

};

And then you would use MockUTManager in your test. This is generally the way to go.

Good luck!

Remco

[Tyler Ross]

Hi Neha,

The way I've typically seen mocks used is when implementing dependency injection. So in your case, it would be when you are testing an object that uses a UTManager; something like:

class TestedObject {

  TestedObject(Element* ut_manager);

  ...

}

In your production code, you would pass a real UTManager:

  ...

  TestedObject tested_object(new UTManager);

  ...

Then, in the test infrastructure, you would pass the mock version:

TEST_F(myTest, foo) {

  TestedObject tested_object(new MockElement);

   ...

}

However, it could be that what you actually need to do in this case is change UTManager so that the dependency or dependencies represented by 'Element' is dependency-injected rather than a base class;

class UTManager {

  UTManager(Element* element);

  ...

 private:

  Element* element_;

}

Then your test would be something like:

TEST_F(TestElementMock, TEST_StartTimer)
{
   MockElement* mockElement = new MockElement();

   EXPECT_CALL(*mockElement, StartTimer(_,_,_))
       .Times(AtLeast(1));

   UTManager* pUTManager = new UTManager(mockElement);

   pUTManager->Initialize();

   pUTManager->HandleTimeout(12);

   delete mockElement;
}

Cheers,

Tyler

On Sat, Jul 10, 2010 at 10:48 AM, Neha Jain <nehaj...@gmail.com> wrote:

--
Tyler Ross | Software Engineer | Google - Apps - Postini

[Neha Jain]

Thanks for your responses Tyler and Remco.

Unfortunately, I cant change the code in this scenario, but will sure keep 'dependency injection' in mind in future.