Mocking objects without no-argument constructor in C# / .NET

Question

Is it possible to create a mock from a class that doesn't provide a no-argument constructor and don't pass any arguments to the constructor? Maybe with creating IL dynamically?

The background is that I don't want to define interfaces only for testing. The workaround would be to provide a no-argument constructor for testing.

question from:https://stackoverflow.com/questions/5262881/mocking-objects-without-no-argument-constructor-in-c-sharp-net

Answer 1

Sure thing. In this example i'll use Moq, a really awesome mocking library.

Example:

public class MyObject
{
     public MyObject(object A, object B, object C)
     {
          // Assign your dependencies to whatever
     }
}

Mock<MyObject> mockObject = new Mock<MyObject>();
Mock<MyObject> mockObject = new Mock<MyObject>(null, null, null); // Pass Nulls to specific constructor arguments, or 0 if int, etc

In many cases though, I assign Mock objects as the arguments so I can test the dependencies:

Mock<Something> x = new Mock<Something>();
MyObject mockObject = new MyObject(x.Object);

x.Setup(d => d.DoSomething()).Returns(new SomethingElse());

etc