Replace a read-only property in a partially mocked object

Question

I am testing an MVC controller that relies on a value returned from a read-only property in a base class.

The getter for this property throws an exception when it is called, since it relies on HttpContext (and other unpleasant things), which I would prefer to avoid ridicule.

This is what I have tried so far:

 controller = Substitute.ForPartsOf<MyController>( Substitute.For<SomeDependency>(), ); controller.UserInfo.Returns(new UserInfo()); 

However, this throws an exception as soon as user access is accessed.

Property in the base class:

 public UserInfo UserInfo { get { // HttpContext dependent stuff } } 

I tried setting the base class property to virtual, but then I got Castle proxy exception.

Answer 1

I think you may have another problem. NSubstitute is able to handle the replacement of virtual properties. Here is a small program that illustrates

 public class SubstitutedClass { public virtual int SubstitutedProperty { get { throw new InvalidOperationException(); } } } internal class Program { private static void Main(string[] args) { var test2 = Substitute.For<SubstitutedClass>(); test2.SubstitutedProperty.Returns(10); Console.WriteLine(test2.SubstitutedProperty); } } 

EDIT: Regarding the use of ForPartsOf , I don’t think it is possible to override a property this way, since there is no way to tell NSubstitute that we don’t want it to call the base code. This is why the documentation mentions that partial sub is not recommended.

You can change the base class to return the value of a virtual function; this virtual function will be replaced. No signature change for callers. Although this is a hack, you will get what you need.

 public class SubstitutedClass { public virtual int SubstitutedProperty { get { return InnerValue(); } } public virtual int InnerValue() { throw new InvalidOperationException(); } } var test2 = Substitute.ForPartsOf<SubstitutedClass>(); test2.When(t => t.InnerValue()).DoNotCallBase(); test2.InnerValue().Returns(10);