GetNumberOfInstances
int numberOfInstances = Item::GetNumberOfInstances();
int newInstances = Item::GetNumberOfInstances() - numberOfInstances;
numberOfInstances = Item::GetNumberOfInstances();
int deletedInstances = numberOfInstances - Item::GetNumberOfInstances();
int numberOfInstances = Item::GetNumberOfInstances();
CPPUNIT_ASSERT_EQUAL(10, Item::GetNumberOfInstances() - numberOfInstances);
CPPUNIT_ASSERT_EQUAL(10, Item::GetNumberOfInstances() - numberOfInstances);
CPPUNIT_ASSERT_EQUAL(0, Item::GetNumberOfInstances() - numberOfInstances);
CPPUNIT_ASSERT_EQUAL(0, Item::GetNumberOfInstances() - numberOfInstances);