Faking live instances

You can use the a.CallTo API to change the behavior of a method in a live (unfaked) object. This allows you to isolate specific parts of the code under test without fully faking the object itself.

Consider the following Person class:

class Person

{

public:

   Address* FillAddress() {return Address::GetFromDatabase();}

   int GetHouseNumber() { FillAddress()->GetHouseNumber();}

...  

}

In this example:

- The FillAddress method interacts with the database to fetch an Address object.

- We want to test the GetHouseNumber method without accessing the database.

To test that the GetHouseNumber method works and returns the default value 1 without accessing the database, we fake only the behavior of the FillAddress method. In this case we do so to return a fake Address.

TEST_F(PersonTests, DefaultHouseNumberIs1)

{

   // Arrange

   auto a = Isolator();  

   Person* person = new Person();

   // Change behavior of a live object

   a.CallTo(person->FillAddress()).WillReturn(new Address("Oxford",1));

   // Act

   auto result = person->GetHouseNumber();

   // Assert

   ASSERT_EQ(1, result);

   delete person;

}

Note that we're creating the Person object with a regular new. It's a standard Person object (not a fake). We then use the same CallTo syntax to ignore the FillAddress call.