I'm writing tests in C++ using googleTest and want to improve them.
I try to describe what I have and what I want to achieve:
I have a class A that has an instance of class B as a member like this:
class ClassA
{
public:
//Some functions
protected:
ClassB m_b;
};
class ClassB
{
void Init(const string &sArgument);
};
In my test I create an instance of ClassA and call a function of it. In this function the function Init() of m_b will be called.
Because Init() of ClassB makes something that I don't want to have in my test I want to call an alternate implementation. My first intention was to create an interface with the function Init() that is implemented by ClassB and by a new class that I create only for the test. Unfortunately to do this I have to create a pointer of the interface and to give it to ClassA.
__interface IB
{
void Init(const string &sArgument);
};
class ClassB : public IB
{
void Init(const string &sArgument) override;
};
class ClassA
{
public:
ClassA(IB* b) : m_b(b){}
//Some functions
protected:
*IB m_b;
};
For my test I create a new class:
class ClassBForTest : public IB
{
void Init(const string &sArgument) override;
};
This is not a good solution so I tried to find another way. What I actually found is the library Isolator++ by Typemock which works quite good. I can say that for all future instances of ClassB the method Init should be replaced with another one. And the best is that I don't have to make any changes in my ClassA. I just have to create a new one:
class ClassBForTest
{
void ISOLATOR_TESTABLE Init(const string &sArgument){}
};
In my test I use this:
ClassBForTest c;
ClassB* b = FAKE_ALL<ClassB>();
WHEN_CALLED(b->Init(ANY_VAL(string))).DoMemberFunctionInstead(&c, Init);
Unfortunately this library is not for free when I want to use it on a build server. So I'm searching for an alternative. As we used gMock in our other tests I tried to realize this with gmock but it didn't work yet. I know that this is not a good statement but I don't want code from you. I only want to know if this is possible with gMock (saying that an alternate implementation should be used without having the instance of ClassB at this point).
Alternatively I ask you for other free libraries I can use.
Thanks a lot in advance,
Michaela
Related
I am trying to run some google tests, and I have quite a lot of code to repeat in each test fixture, so I want to make the code as brief as possible, and I would like to use the SetUp method of the child class of Testing::test parent class, but the TEST_F fixtures do not recognize the variables from SetUp
This is the simplest example I can come up with:
class FooTest: public testing::Test
{
protected:
virtual void SetUp() // using void SetUp() override does not help
{
int FooVar = 911;
}
virtual void TearDown()
{
}
};
TEST_F(FooTest, SampleTest)
{
// FooTest::SetUp(); // This does not help as well
EXPECT_EQ(911, FooVar);
}
When I try to compile this code it shows an error that FooVar was not declared in this scope. How can I fix it?
Thank you very much for any help.
FooVar is a local variable inside the SetUp method. If you want to use it in the test fixtures, it needs to be a class member:
class FooTest: public testing::Test
{
protected:
int FooVar;
virtual void SetUp() override
{
this.FooVar = 911;
}
};
In this example, if you are only setting integral types, should just make them const member variables.
I have some C++ code as follows:
class MyClass
{
public:
MyClass(OtherClass *obj)
{
obj_ = obj;
}
void myMethod()
{
// Do something
int value = obj_->otherMethod();
// Do something else
}
private:
OtherClass *obj_;
}
I want to create a unit test to test the functionality of myMethod(). Unfortunately, OtherClass is an external library and its methods are not declared virtual (so I can't inherit the methods and stub them out in a mock). I have some experience with Mockito where I might have used a spy for this purpose. But I can't seem to find an equivalent in C++.
I'm using the googletest framework for now and the context for this question (if it helps) is in ROS, where I'm actually trying to stub out tf::TransformListener.
Question 1: Is there an alternative to spies that I might not know of and can leverage in this situation?
Question 2: If there isn't, is there a quick-and-easy way for me to restructure my code so that I can leverage a mock?
Solved by doing the following:
class IOtherMethodAdapter
{
public:
virtual int otherMethod() = 0;
}
class OtherClassOtherMethodAdapter : public IOtherMethodAdapter
{
public:
int otherMethod() { return obj_->otherMethod(); }
private:
OtherClass *obj_;
}
Now I use a pointer to IOtherMethodAdapter in MyClass instead of OtherClass and for testing I simply initialize the implementation of the interface to a stubbed/mock object. If there is another way, feel free to post that solution too.
I have certain functionality encapsulated in classes which I use in another class. I think this is called composition.
class DoesSomething01
{
public:
DoesSomething01();
void functionality01();
void functionality02();
};
class DoesSomething02
{
public:
DoesSomething02();
void functionality01();
void functionality02();
};
class ClassA
{
public:
ClassA();
private:
DoesSomething01 *m_doesSomething01;
DoesSomething02 *m_doesSomething02;
};
If I have now a ClassB which "knows" ClassA and have to use/execute functionality01 and/or functionality02 of classes DoesSomething01 and/or DoesSomething02 I see two possibilities:
a) Add methods like this to ClassA to provide ClassB direct access to DoesSomething01 and/or DoesSomething02:
DoesSomething01 *getDoesSomething01() { return *m_doesSomething01; }
DoesSomething02 *getDoesSomething02() { return *m_doesSomething02; }
ClassB could then do something like this:
m_classA->getDoesSomething01()->functionality01();
b) Add (in this case four) methods to ClassA which forwards the method calls to DoesSomething01 and DoesSomething02 like this:
void doesSomething01Functionality01() { m_doesSomething01->functionality01(); }
void doesSomething01Functionality02() { m_doesSomething01->functionality02(); }
void doesSomething02Functionality01() { m_doesSomething02->functionality01(); }
void doesSomething02Functionality02() { m_doesSomething02->functionality02(); }
Which option is better and why?
What are the advantages/disadvantages of each option?
First option can be considered a code smell. According to Robert C. Martin's 'Clean Code' it is "Transitive Navigation" and should be avoided. Quoting the author:
In general we don’t want a single module to know much about its
collaborators. More specifically, if A collaborates with B, and B
collaborates with C, we don’t want modules that use A to know about C.
(For example, we don’t want a.getB().getC().doSomething();.)
Second option looks better. It is classical use of Facade pattern. And it is better, because it hides other functionalities of classes DoesSomthing01 and DoesSomthing02. Then you ve'got simplified view of it which is easier to use than 1st option.
Edit: there is also one more thing. You've got two classes which have the same functionalites and are aggregated by other class. You should consider using Stratey pattern here. The your code will look like this:
class DoesSomething
{
public:
virtual void functionality01() = 0;
virtual void functionality02() = 0;
}
class DoesSomething01 : DoesSomething
{
public:
DoesSomething01();
void functionality01();
void functionality02();
};
class DoesSomething02 : DoesSomething
{
public:
DoesSomething02();
void functionality01();
void functionality02();
};
class ClassA
{
public:
ClassA();
DoesSomething* doesSomething(); // Getter
void doesSomething(DoesSomething* newDoesSomething); // Setter
// ...
private:
DoesSomething *m_doesSomething;
};
Then you will need only two method instead of four:
void doesFunctionality01() { m_doesSomething->functionality01(); }
void doesFunctionality02() { m_doesSomething->functionality02(); }
The first scenario is a violation of law of Demeter, which says that a class can only talk to its immediate friends. Basically the problem with the first approach is that any change in the inner classes DoSomething01 and DoSomething02 will trigger a change in Class A as well as Class B because both classes are now directly dependent on these inner classes.
The second option is better as it encapsulates the class B from inner classes but a side effect of this solution is that now class A has a lot of methods that does nothing fancy except for delegating to its inner classes. This is fine but imagine if DoSomething01 has an inner class DoSomething03 and class B needs to access its functionality without directly knowing about it than the class A would need to have another method that would delegate to DoSomething01 that would in turn delegate to DoSomething03. In this case I think it is better to let class B directly know about DoSomething01 otherwise class A is going to have a huge interface that simply delegates to its inner classes.
If there are many classes and/or many methods to be called it makes sense to invent
an interface in the form of an abstract parent class:
class SomeInterface
{
public:
SomeInterface(){}
virtual void functionally01() = 0;
virtual void functionally02() = 0;
}
DoesSomthing01 and other classes would then inherit this class:
class DoesSomthing01 : public SomeInterface
and implement the methods.
If it make sense to associate a key with the instantiation of such a class
you could store these objects in ClassA e.g. using a map (here I
use an integer as the key):
class ClassA
{
private:
std::map<int, SomeInterface*> m_Interfaces;
public:
SomeInterface* getInterface(const int key)
{
std::map<int, SomeInterface*>::iterator it(m_Interfaces.find(key));
if (it != m_Interfaces.end())
return it->second;
else
return NULL;
}
};
From ClassB you could then access them
int somekey = ...;
SomeInterface *myInter = m_classA->getInterface(somekey);
if (myInter)
myInter->functionally01();
This way you have just one access method (getInterface()) independent
of the number of objects.
In order to encode the access to the methods using a key you could
create a map which maps a key onto a closure or a simple switch statement:
in SomeInterface:
public:
void executeMethod(const int key)
{
switch(key)
{
case 1: functionally01(); break;
case 2: functionally01(); break;
default:
// error
}
int methodKey = ...;
int objectKey = ...;
SomeInterface *myInter = m_classA->getInterface(objectKey);
if (myInter)
myInter->executeMethod(methodKey);
Looks like a good case for a Mediator Pattern.
This pattern manage communication between 2 objects that he owns.
There probably is a fairly simple and straight-forward answer for this, but for some reason I can't see it.
I need to restrict calling methods from a class only to some methods implemented by derived classes of some interface.
Say I have
class A{
public:
static void foo();
};
class myInterface{
public:
virtual void onlyCallFooFromHere() = 0;
}
class myImplementation : public myInterface{
public:
virtual void onlyCallFooFromHere()
{
A::foo(); //this should work
}
void otherFoo()
{
A::foo(); //i want to get a compilation error here
}
}
So I should be able to call A::foo only from the method onlyCallFooFromHere()
Is there a way to achieve this? I'm open to any suggestions, including changing the class design.
EDIT:
So... I feel there's a need to further explain the issue. I have a utility class which interacts with a database (mainly updates records) - class A.
In my interface (which represents a basic database objects) I have the virtual function updateRecord() from which I call methods from the db utility class. I want to enforce updating the database only in the updateRecord() function of all extending classes and nowhere else. I don't believe this to be a bad design choice, even if not possible. However, if indeed not possible, I would appreciate a different solution.
Change the class design - what you want is impossible.
I am unsure of what you are trying to achieve with so little details and I am unable to comment further.
[Disclaimer: this solution will stop Murphy, not Macchiavelli.]
How about:
class DatabaseQueryInterface {
public:
~virtual DatabseQueryInterface() = 0;
virtual Query compileQuery() const = 0; // or whatever
virtual ResultSet runQuery(const Query&) const = 0; // etc
};
class DatabaseUpdateInterface : public DatabaseQueryInterface {
public:
virtual Update compileUpdate() const = 0; // whatever
};
class DatabaseObject {
public:
virtual ~DatabaseObject() = 0;
protected:
virtual void queryRecord(const DatabaseQueryInterface& interface) = 0;
virtual void updateRecord(const DatabaseUpdateInterface& interface) = 0;
};
class SomeConcreteDatabaseObject : public DatabaseObject {
protected:
virtual void updateRecord(const DatabaseUpdateInterface& interface) {
// gets to use interface->compileUpdate()
}
virtual void queryRecord(const DatabaseQueryInterface& interface) {
// only gets query methods, no updates
}
};
So the basic idea is that your DatabaseObject base class squirrels away a private Query object and a private Update object and when it comes time to call the protected members of the subclass it hands off the Update interface to the updateRecord() method, and the Query interface to the queryRecord() method.
That way the natural thing for the subclasses is to use the object they are passed to talk to the database. Of course they can always resort to dirty tricks to store away a passed-in Update object and try to use it later from a query method, but frankly if they go to such lengths, they're on their own.
You could split your project into different TUs:
// A.h
class A
{
public:
static void foo();
};
// My.h
class myInterface
{
public:
virtual void onlyCallFooFromHere() = 0;
}
class myImplementation : public myInterface
{
public:
virtual void onlyCallFooFromHere();
void otherFoo();
};
// My-with-A.cpp
#include "My.h"
#include "A.h"
void myImplementation::onlyCallFooFromHere() { /* use A */ }
// My-without-A.cpp
#include "My.h"
void myImplementation::otherFoo() { /* no A here */ }
You probably know this, but with inheritance, you can have public, protected, and private member access.
If a member is private in the base class, the derived cannot access it, while if that same member is protected, then the derived class can access it (while it still isn't public, so you're maintaining encapsulation).
There's no way to stop specific functions from being able to see whats available in their scope though (which is what you're asking), but you can design your base class so that the derived classes can only access specific elements of it.
This could be useful because class B could inherit from class A as protected (thus getting its protected members) while class C could inherit from the same class A as public (thus not getting access to its protected members). This will let you get some form of call availability difference at least -- between classes though, not between functions in the same class.
This could work.
class myInterface;
class A {
private:
friend class myInterface;
static void foo();
};
class myInterface {
public:
virtual void onlyCallFooFromHere() {callFoo();}
protected:
void callFoo() {A::foo();}
};
Though at this point I think I'd just make A::foo a static of myInterface. The concerns aren't really separate anymore.
class myInterface {
protected:
static void foo();
};
Is there a reason foo is in A?
EDIT: minor fixes (virtual Print; return mpInstance) following remarks in the answers.
I am trying to create a system in which I can derive a Child class from any Base class, and its implementation should replace the implementation of the base class.
All the objects that create and use the base class objects shouldn't change the way they create or call an object, i.e. should continue calling BaseClass.Create() even when they actually create a Child class.
The Base classes know that they can be overridden, but they do not know the concrete classes that override them.
And I want the registration of all the the Child classes to be done just in one place.
Here is my implementation:
class CAbstractFactory
{
public:
virtual ~CAbstractFactory()=0;
};
template<typename Class>
class CRegisteredClassFactory: public CAbstractFactory
{
public:
~CRegisteredClassFactory(){};
Class* CreateAndGet()
{
pClass = new Class;
return pClass;
}
private:
Class* pClass;
};
// holds info about all the classes that were registered to be overridden
class CRegisteredClasses
{
public:
bool find(const string & sClassName);
CAbstractFactory* GetFactory(const string & sClassName)
{
return mRegisteredClasses[sClassName];
}
void RegisterClass(const string & sClassName, CAbstractFactory* pConcreteFactory);
private:
map<string, CAbstractFactory* > mRegisteredClasses;
};
// Here I hold the data about all the registered classes. I hold statically one object of this class.
// in this example I register a class CChildClass, which will override the implementation of CBaseClass,
// and a class CFooChildClass which will override CFooBaseClass
class RegistrationData
{
public:
void RegisterAll()
{
mRegisteredClasses.RegisterClass("CBaseClass", & mChildClassFactory);
mRegisteredClasses.RegisterClass("CFooBaseClass", & mFooChildClassFactory);
};
CRegisteredClasses* GetRegisteredClasses(){return &mRegisteredClasses;};
private:
CRegisteredClasses mRegisteredClasses;
CRegisteredClassFactory<CChildClass> mChildClassFactory;
CRegisteredClassFactory<CFooChildClass> mFooChildClassFactory;
};
static RegistrationData StaticRegistrationData;
// and here are the base class and the child class
// in the implementation of CBaseClass::Create I check, whether it should be overridden by another class.
class CBaseClass
{
public:
static CBaseClass* Create()
{
CRegisteredClasses* pRegisteredClasses = StaticRegistrationData.GetRegisteredClasses();
if (pRegisteredClasses->find("CBaseClass"))
{
CRegisteredClassFactory<CBaseClass>* pFac =
dynamic_cast<CRegisteredClassFactory<CBaseClass>* >(pRegisteredClasses->GetFactory("CBaseClass"));
mpInstance = pFac->CreateAndGet();
}
else
{
mpInstance = new CBaseClass;
}
return mpInstance;
}
virtual void Print(){cout << "Base" << endl;};
private:
static CBaseClass* mpInstance;
};
class CChildClass : public CBaseClass
{
public:
void Print(){cout << "Child" << endl;};
private:
};
Using this implementation, when I am doing this from some other class:
StaticRegistrationData.RegisterAll();
CBaseClass* b = CBaseClass::Create();
b.Print();
I expect to get "Child" in the output.
What do you think of this design? Did I complicate things too much and it can be done easier? And is it OK that I create a template that inherits from an abstract class?
I had to use dynamic_pointer (didn't compile otherwise) - is it a hint that something is wrong?
Thank you.
This sort of pattern is fairly common. I'm not a C++ expert but in Java you see this everywhere. The dynamic cast appears to be necessary because the compiler can't tell what kind of factory you've stored in the map. To my knowledge there isn't much you can do about that with the current design. It would help to know how these objects are meant to be used. Let me give you an example of how a similar task is accomplished in Java's database library (JDBC):
The system has a DriverManager which knows about JDBC drivers. The drivers have to be registered somehow (the details aren't important); once registered whenever you ask for a database connection you get a Connection object. Normally this object will be an OracleConnection or an MSSQLConnection or something similar, but the client code only sees "Connection". To get a Statement object you say connection.prepareStatement, which returns an object of type PreparedStatement; except that it's really an OraclePreparedStatement or MSSQLPreparedStatement. This is transparent to the client because the factory for Statements is in the Connection, and the factory for Connections is in the DriverManager.
If your classes are similarly related you may want to have a function that returns a specific type of class, much like DriverManager's getConnection method returns a Connection. No casting required.
The other approach you may want to consider is using a factory that has a factory-method for each specific class you need. Then you only need one factory-factory to get an instance of the Factory. Sample (sorry if this isn't proper C++):
class CClassFactory
{
public:
virtual CBaseClass* CreateBase() { return new CBaseClass(); }
virtual CFooBaseClass* CreateFoo() { return new CFooBaseClass();}
}
class CAImplClassFactory : public CClassFactory
{
public:
virtual CBaseClass* CreateBase() { return new CAImplBaseClass(); }
virtual CFooBaseClass* CreateFoo() { return new CAImplFooBaseClass();}
}
class CBImplClassFactory : public CClassFactory // only overrides one method
{
public:
virtual CBaseClass* CreateBase() { return new CBImplBaseClass(); }
}
As for the other comments criticizing the use of inheritance: in my opinion there is no difference between an interface and public inheritance; so go ahead and use classes instead of interfaces wherever it makes sense. Pure Interfaces may be more flexible in the long run but maybe not. Without more details about your class hierarchy it's impossible to say.
Usually, base class/ derived class pattern is used when you have an interface in base class, and that interface is implemented in derived class (IS-A relationship). In your case, the base class does not seem to have any connection with derived class - it may as well be void*.
If there is no connection between base class and derived class, why do you use inheritance? What is the benefit of having a factory if factory's output cannot be used in a general way? You have
class CAbstractFactory
{
public:
virtual ~CAbstractFactory()=0;
};
This is perfectly wrong. A factory has to manufacture something that can be used immediately:
class CAbstractFactory
{
public:
virtual ~CAbstractFactory(){};
public:
CBaseClass* CreateAndGet()
{
pClass = new Class;
return pClass;
}
private:
CBaseClass* pClass;
protected:
CBaseClass *create() = 0;
};
In general, you're mixing inheritance, virtual functions and templates the way they should not be mixed.
Without having read all of the code or gone into the details, it seems like you should've done the following:
make b of type CChildClass,
make CBaseClass::Print a virtual function.
Maybe I'm wrong but I didn't find any return statement in your CBaseClass::Create() method!
Personally, I think this design overuses inheritance.
"I am trying to create a system in which I can derive a Child class from any Base class, and its implementation should replace the implementation of the base class." - I don't know that IS-A relationships should be that flexible.
I wonder if you'd be better off using interfaces (pure virtual classes in C++) and mixin behavior. If I were writing it in Java I'd do this:
public interface Foo
{
void doSomething();
}
public class MixinDemo implements Foo
{
private Foo mixin;
public MixinDemo(Foo f)
{
this.mixin = f;
}
public void doSomething() { this.mixin.doSomething(); }
}
Now I can change the behavior as needed by changing the Foo implementation that I pass to the MixinDemo.