How do I mock a class without an interface

Question

I am working on  NET 4 0 using C  in Windows 7    I want to test the communication between some methods using mock  The only problem is that I want to do it without implementing an interface  Is that possible    I just read a lot of topics and some tutorials about mock objects  but all of them used to mock interfaces  and not the classes  I tried to use Rhino and Moq frameworks

User · Answer

Most mocking frameworks  Moq and RhinoMocks included  generate proxy classes as a substitute for your mocked class  and override the virtual methods with behavior that you define   Because of this  you can only mock interfaces  or virtual methods on concrete or abstract classes   Additionally  if you re mocking a concrete class  you almost always need to provide a parameterless constructor so that the mocking framework knows how to instantiate the class   Why the aversion to creating interfaces in your code

User · Answer

The standard mocking frameworks are creating proxy classes  This is the reason why they are technically limited to interfaces and virtual methods   If you want to mock  normal  methods as well  you need a tool that works with instrumentation instead of proxy generation  E g  MS Moles and Typemock can do that  But the former has a horrible  API   and the latter is commercial

User · Answer

If worse comes to worse  you can create an interface and adapter pair  You would change all uses of ConcreteClass to use the interface instead  and always pass the adapter instead of the concrete class in production code   The adapter implements the interface  so the mock can also implement the interface    It s more scaffolding than just making a method virtual or just adding an interface  but if you don t have access to the source for the concrete class it can get you out of a bind

User · Answer

I think it s better to create an interface for that class  And create a unit test using interface   If it you don t have access to that class  you can create an adapter for that class   For example   public class RealClass       int DoSomething string input                   real implementation here          public interface IRealClassAdapter       int DoSomething string input      public class RealClassAdapter   IRealClassAdapter       readonly RealClass  realClass       public RealClassAdapter     gt   realClass   new RealClass         int DoSomething string input    gt   realClass DoSomething input       This way  you can easily create mock for your class using IRealClassAdapter    Hope it works

User · Answer

I faced something like that in one of the old and legacy projects that i worked in that not contains any interfaces or best practice and also it s too hard to enforce them build things again or refactoring the code due to the maturity of the project business  So in my UnitTest project i used to create a Wrapper over the classes that I want to mock and that wrapper implement interface which contains all my needed methods that I want to setup and work with  Now I can mock the wrapper instead of the real class   For Example   Service you want to test which not contains virtual methods or implement interface  public class ServiceA   public void A      public String B          Wrapper to moq  public class ServiceAWrapper   IServiceAWrapper   public void A      public String B          The Wrapper Interface  public interface IServiceAWrapper   void A     String B         In the unit test you can now mock the wrapper       public void A Run ChangeStateOfX             var moq   new Mock lt IServiceAWrapper gt         moq Setup               This might be not the best practice  but if your project rules force you in this way  do it  Also Put all your Wrappers inside your Unit Test project or Helper project specified only for the unit tests in order to not overload the project with unneeded wrappers or adaptors   Update  This answer from more than a year but in this year i faced a lot of similar scenarios with different solutions  For example it s so easy to use Microsoft Fake Framework to create mocks  fakes and stubs and even test private and protected methods without any interfaces   You can read  https   docs microsoft com en-us visualstudio test isolating-code-under-test-with-microsoft-fakes view vs-2017

User · Answer

If you cannot change the class under test  then the only option I can suggest is using MS Fakes https   msdn microsoft com en-us library hh549175 aspx  However  MS Fakes works only in a few editions of Visual Studio

User · Answer

Simply mark any method you need to fake as virtual  and not private    Then you will be able to create a fake that can override the method    If you use new Mock lt Type gt  and you don t have a parameterless constructor then you can pass the parameters as the arguments of the above call as it takes a type of param Objects

User · Answer

With MoQ  you can mock concrete classes   var mocked   new Mock lt MyConcreteClass gt       but this allows you to override virtual code  methods and properties

[c#] How do I mock a class without an interface?

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