Moq and Code Contracts

Question

When using class invariants, Code contracts seems to inject code everywhere. Stuff like this

[ContractClassFor(typeof(IX))]
interface IXContract  
{  
    [ClassInvariant]
    void Invariant() { ... }
}

[ContractClass(typeof(IXContract))]
interface IX { event EventHandler b; }

var a = new Mock<IX>();

a.Raise(x => x.b += null);

Fails with an error message

Could not locate event for attach or detach method Void $InvariantMethod$().

Anyone know of a solution?

@jameszhao00 Its been a while, have any of the answers helped you? — Andy, Mar 10 '12 at 01:34

score 3 · Answer 1 · answered Nov 11 '11 at 17:55

This unit test "passes" when run without generating exceptions:

[ContractClassFor(typeof(IX))]
class IXContract
{
    [ContractInvariantMethod]
    void Invariant() { }
}

[ContractClass(typeof(IXContract))]
public interface IX { event EventHandler b; }

/// <summary>
/// Summary description for UnitTest1
/// </summary>
[TestClass]
public class UnitTest1
{
    public void MyTest()
    {
        var a = new Mock<IX>();

        a.Raise(x => x.b += null);
    }
}

I'm not entirely sure what's going on and how you're compiling (or transcribing) the above, but I don't think you can have "ContractClassFor" attribute decorating an interface, and you certainly can't have the implementation "{ ... }" in an interface. You also need to make your interface IX public to mock it (or else internal with InternalsVisibleTo() castle proxy in your properties).

Hopefully this helps, but feel free to update your post with new code if this doesn't lead you toward what you're looking to do.

There's a few things wrong with your changes too. IXContract should be abstract, not just internal. The Invariant method isn't appropriate there. Having one isn't really possible as you're checking properties and fields of the implmentation, and you dont know how everyone will implment the interface. Also this Contract class is NOT the actual implemenation, its there as glue to allow contracts on interfaces. Also, the class MUST implement the IX interface. See my answer for what it should look like. — Andy, Jan 09 '12 at 17:19

score 2 · Answer 2 · answered Jan 09 '12 at 17:13

Your code is incorrect. It should look like this:

[ContractClassFor(typeof(IX))] 
internal abstract class XContract : IX
{   
    // Invariants belong on your actual implemenation; interfaces don't dictate implemenation so this isn't appropariate here.
    // [ ContractInvariantMethod] 
    // void Invariant() { ... } 

    public event EventHandler b { get { return default(EventHandler); } set { }}
} 

[ContractClass(typeof(XContract))] 
interface IX { event EventHandler b; } 

var a = new Mock<IX>(); 

a.Raise(x => x.b += null);

Notice that the Contract class is Internal Abstract, and that it also now implements your interface. The Invariant isn't appropiate there, as that's for implemenation details; you don't know how people will implemenent your interface, so don't put it there. Also the attribute for invariant methods is ContractInvariantMethodAttribute.

Moq and Code Contracts

2 Answers2

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