How to use gmock to mock up a std::function?

Question

The constructor of my class is

A( ...
   std::function<bool(const std::string&, const std::string&)> aCallBack, 
   ... );

I want to use EXPECT_CALL to test it. This callback is from another class B. I created a Mock like

class BMock : public B
{
    MOCK_METHOD2( aCallBack, bool(const std::string&, const std::string&) );
}

Then I tried

B *b = new B();
std::function<bool(const std::string&, const std::string&)> func = 
    std::bind(&B::aCallBack, b, std::PlaceHolders::_1, std::PlaceHolders::_2);

It still does not work. How can I get a function pointer of a gmock object?

Thanks!!

Vickyvico

Answer 1

If you want to use mock to keep track of calls and set return values, you can use MockFunction.

using testing::_;
using testing::MockFunction;
using testing::Return;

MockFunction<bool(const std::string&, const std::string&)> mockCallback;

EXPECT_CALL(mockCallback, Call(_, _)).WillOnce(Return(false)); // Or anything else you want to do

A( ...
   mockCallback.AsStdFunction()
   ...);

Consanguineous

This is golden. Been looking for this across multiple related stack overflow posts, and your answer was the first I found that mentioned MockFunction and provided a complete example. – Six

I am not sure why this was never mentioned in the documentation. Am I missing something? – Cockspur

It's documented in Cookbook at least - github.com/google/googletest/blob/master/googlemock/docs/… – Consanguineous

Unfortunately, all MockFunctions are identified as Call in error messages which is very unhelpful... – Chan

Answer 2

With unit testing you should only test your class A so your test should just check if any function passed to the constructor gets called. So you don't need a mock, instead just pass a lambda that just record with a boolean (or a counter).

bool gotCalled = false;
A a( [&gotCalled]( const std::string&, const std::string& ) { gotCalled = true; return true; } );
...
ASSERT_TRUE( gotCalled );

Delegate

Anyway, although it's fine passing a function to the constructor, architecturally it doesn't smell right if it's used as callback. Generally it would be better to pass it to the function that actually is using it. – Delegate

this answer has nothing to do with an actual solution to TS problem, for the actual answer please check Enzam's answer – Kurtz