How to make class more testable?

Question

I have this:

 class FooGenerator:IFooGenerator {
      private object _generated;

      public void Generate() {
         // Generating
         GenerateSmallPart();
         GenerateOtherSmallPart();
         GenerateTinyPart();
         // A lot similar
      }

      private void GenerateSmallPart() {
         //add small part to _generated
      }

      private void GenerateOtherSmallPart() {
         //add small part to _generated
      }

      private void GenerateTinyPart() {
         //add small part to _generated
      }
   }

   internal interface IFooGenerator {
      void Generate();
   }

In my application I use only IFooGenerator via IoC but I want to test all those sub methods.

As I found here, one option is to extract class with all sub methods. But why do i need to do that. It is only being used in FooGenerator.

Do you have any suggestions how can i make my class more testable?

Answer 1

I will share with you how I usually handle this situation. If I see that I want to test some private methods for some reason (like it is hard to stub input parameters to test all code flows) - this usually means for me that complexity of my class is high and I need to refactor my code. In your case (I have no idea what your methods are doing) you can use something like:

interface IPartGenerator
{
   void GeneratePart();
}

class SmallPartGenerator : IPartGenerator
{
   void GeneratePart();
}

class OtherSmallPartGenerator : IPartGenerator
{
   void GeneratePart();
}

class TinyPartGenerator : IPartGenerator
{
   void GeneratePart();
}

class FooGenerator:IFooGenerator 
{
   private IPartGenerator[] partGenerators = new IPartGenerator[] 
                        {
                           new SmallPartGenerator(), 
                           new OtherSmallPartGenerator(), 
                           new TinyPartGenerator ()
                        }

   public void Generate()
   {
        foreach (var partGenerator in partGenerators)
        {
              partGenerator.GeneratePart();
        }
   }
}

Now you can test each of the part generators separately.

Answer 2

Who is the client?

Many people (Roy Osherove, Michael Feathers) consider the test client just as valid as the interface or service client.

With that in mind I think it's fine to slightly go against the principle of encapsulation by opening up testable seams by making some private methods public.