You have public methods not implementing an interface - reidev275/SignsYouShouldProbablyRefactor GitHub Wiki

Example

interface IBaker
{
 void Bake();
}

class PizzaBaker : IBaker
{
 public void Bake() { ... }
 public void AddToppings() { ... }
}

Why is this bad?

1. If we have any code that actually calls AddToppings we are probably breaking the Liskov Substitution Principal.
2. Code that calls the non interface method must be dealing with the concrete class rather than utilizing polymorphism.

Resolved

We could choose to add a method to IBaker or we could create a new interface. I like [Role-based interfaces] (http://martinfowler.com/bliki/RoleInterface.html), so I created a new interface so that the Interface Segregation Principal is followed.

interface IBaker
{
  void Bake();
}

interface IPizzaTopper
{
  void AddToppings();
}

class PizzaBaker : IBaker, IPizzaTopper
{
  public void Bake() { ... }
  public void AddToppings() { ... }
}