Frozen mock's property is getting overwritten

Question

I'm having an issue where AutoFixture seems to be overwriting a property on a frozen mock. The property on the mocked class is read-only, and from what I've read, AutoFixture shouldn't be trying to do anything with it.

I've included code to reproduce the issue in LINQPad below. Victim is a trivial test class with two read-only properties. At issue is that once I have set the expectation for the Things property and registered the mock's Object as the instance for AutoFixture to return for the Victim type, the collection Things contains different strings.

To reproduce the problem, run the code below in LINQPad as a C# Program and reference AutoFixture and Moq from NuGet. Be sure to include the namespaces Moq and Ploeh.AutoFixture.

My expectation is that I should get back the object I registered with Register and that the collection Things in the returned Victim should return the collection I referenced in my call to SetupGet.

public class Victim
{
    private string _vic;
    private IEnumerable<string> _things;
    public virtual string VictimName { get { return _vic; } }
    public virtual IEnumerable<string> Things { get { return _things; } }
}

void Main()
{
    var fixture = new Fixture();
    var victimName = fixture.CreateAnonymous("VIC_");
    var things = fixture.CreateMany<string>();
    victimName.Dump("Generated vic name");
    things.Dump("Generated things");

    var victimMock = fixture.Freeze<Mock<Victim>>();
    victimMock.SetupGet(x => x.VictimName).Returns(victimName).Verifiable();
    victimMock.SetupGet(x => x.Things).Returns(things).Verifiable();
    fixture.Register(() => victimMock.Object);

    var victim = fixture.CreateAnonymous<Victim>();
    (victim.Equals(victimMock.Object)).Dump("Victims are the same?");
    victim.VictimName.Dump("Returned name");
    victim.Things.Dump("Returned things");
    (things.Equals(victim.Things)).Dump("Returned things are the same?");

    victimMock.Verify();
}

Answer 1

My guess is that the Iterator for Things is actually the same, but that the strings it generates are different. This is actually by design, although we've later come to realize that this wasn't a particularly good design decision.

In AutoFixture 3, this behavior has been changed.

If I've guessed correctly, this issue will go away in AutoFixture 3. In AutoFixture 2 you should be able to resolve it by creating the fixture like this:

var fixture = new Fixture().Customize(new StableMultipeCustomization());