Solution 2a: Visitable Mock Objects With Macros

In the previous example each sub-expectation was created and adjusted manually. To reduce the code needed to set up the desired behaviour mockpp provides advanced mock objects. One of them uses the visitable approach. The name is derived from the fact that the behaviour is set up using some king of recording machanism, or by visting the mock object.

First the a container mock object must be implemeneted. Similar to the first solution is must inherit from Interface and from VisitableMockObject . All the functionality is hidden in internal variables and helper methods. There is a set of variables for each method which must be initialized in the constructor. This work is done with a macro. The macro name depends on the type of method and the number of parameters it takes. You can read more about the details in the handbook.

class VisitMock : public Interface
                , public VisitableMockObject

      : VisitableMockObject("VisitMock", 0)

Then the methods are implemented. The according code for the variables and helper methods is also hidden in macros. In the simplest case you only have to pick the according macro and add the name of the class and the method. So the definition for method close() is easy:

    MOCKPP_VOID_VISITABLE0(VisitMock, close);

If the method has a non standard type (according to the definition of mockpp) you need an extended set of macros. The same applies to overloaded methods. This is necessary because the internal variables and names are derived from the methods name and parameters but need special handling. This is also explained in the according section of the handbook.

    MOCKPP_VOID_VISITABLE_EXT1(VisitMock, open, const std::string &,
                                          ext,  std::string);

Once the class is finished and ready to use the desired behaviour must be set up. This is done by invoking the expected methods with the expected parameters. In the example the file is opened, three lines are read and the file is closed.

    VisitMock mock;"file1.lst");;;;

When you want to prepare the return values for the method read() you use a helper object which passes the values via helper methods in the desired order into the mock object.

    MOCKPP_CONTROLLER_FOR(VisitMock, read) read_controller (&mock);


After all the behaviour is added you have to switch the mock object into test mode by invoking activate() . Then you run the methods under test. Similar to the first example you should call verify() at the end to check for pending expectations.


    Consumer consumer(&mock);

  catch(std::exception &ex)
    std::cout << std::endl
              << "Error occured.\n" << ex.what() << std::endl
              << std::endl;

visitmock.cpp contains the complete source code.

Enhanced functionality

Visitable mock objects offer some more functionality. Suppose you have a method add() which receives two parameters and returns the sum.You could emulate this behaviour for some expected values by using the following statements. Additionally the method shall return -1 as error indicator for all other parameters. As an alternative you could have it throw an exception by using setDefaultThrowable().

    MOCKPP_CONTROLLER_FOR(VisitMock, add) add_controller (&mock);

    add_controller.addResponseValue(3, 1, 2);      // 1 and 2 are expected
    add_controller.addResponseValue(110, 99, 11);  // 99 and 11 are expected

Another rather common problem is the simulation of runtime errors. Such errors happen usually when you don't expect them but you hardly can reproduce them. To address such testing problems you might use a Throwable . The following code could be used to emulate a method that returns bytes from a network connection. The first 10 calls return 0, but the next call throws a NetworkError . All the following calls return 1.

    class NetworkError {};

    MOCKPP_CONTROLLER_FOR(VisitMock, network_read) read_controller (&mock);

    read_controller.addReturnValue(0, 10);

When generating such behaviour you should keep in mind that there is a determined dispatching order which is explained in the VisitableMockObject section of the handbook.

Since the parameters passed to calculate are not exactly defined we must implement some tolerance. This can be achieved with an according constraint. In this case IsCloseTo which allows a delta value.


Another constraint is used to verify the data that is written back. The important part is the appended string "processed" so only this substring is verified:


In a similar manner the return value can be influenced by passing the controller object according constraints instead of exact values.

    calculate_controller.addResponseValue(10, eq<unsigned>(2,2));
    calculate_controller.addResponseValue(20, eq<unsigned>(4,2));
    calculate_controller.addResponseValue(30, eq<unsigned>(6,2));

visitmock.cpp contains the complete source code.

Next: Solution 2b: Visitable Mock Methods

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