when calling PRIVATE_WHEN_CALLED the function could not be found

the class in hpp is:

class ComposedClass
{
public:
    int getComposedData();
};

class POCClassForTypeMock
{
public:
    int callGetNumber();
    int getComposedData();

private:
    ComposedClass mComposedClass;
    int getNumber();
};

the test is:

TEST_CASE("Testing private Search")

{

    POCClassForTypeMock * obj = new POCClassForTypeMock;

    PRIVATE_WHEN_CALLED(obj, getNumber).Return(0);

    REQUIRE(obj->callGetNumber() == 0);

    delete obj;

}

got error message:

- The function 'POCClassForTypeMock::getNumber' could not be found. If the method is not called in the code under test it will be optimized away. Remove any inline keywords, and Add ISOLATOR_TESTABLE to the method.

looks like it doesn't recognize private functions.

this example works fine in your standalone