StackOverflow in .NET unit testing when references are circular

Question

I was testing something else for circular reference resistance when I noticed:

    public class Foo
    {
        private Bar myBar = new Bar();
    }

    public class Bar
    {
        private Foo myFoo = new Foo();
    }

    [Fact]
    public void CircularReferenceTest()
    {
        var foo = new Foo();
        var bar = new Bar();
    }

resulted in XUnit runner halt and console log:

The active test run was aborted. Reason: Process is terminated due to StackOverflowException.

I tested it on MStest and had same result. Is there a way around this? Is it a bug, or it's intended to stop execution in that way?

You're not testing anything. And why wouldn't you expect a Stack Overflow with your code? — Steve, Jan 22 '18 at 23:49
I posted minimal example that yields SO as a proof. I am testing circular reference guard, so I need the above to pass along. — Piotr Falkowski, Jan 22 '18 at 23:51
@Piotr Falkowski Are you saying that this one test should fail, but the remaining tests should run? — Andrew Shepherd, Jan 22 '18 at 23:55
This one should pass. I do not see a reason why it is not. I am also expecting GC to handle circular references correctly and for what I know it does — Piotr Falkowski, Jan 22 '18 at 23:57

score 9 · Accepted Answer · answered Jan 22 '18 at 23:58

you are not making circular reference. you are making bunch of references pointing one to another (linked list if you say), eventually it causes Stack overflow exception because stack becomes full.

Here is how to make circular reference. I don't think you can leave fields private, because two classes must somehow know each other at some point. (i.e at some point this connection must be made)

public class Foo
{
    public Bar MyBar { get; set; }  
}

public class Bar
{
    public Foo MyFoo { get; set; } 
}

public void CircularReferenceTest()
{
    var foo = new Foo();
    var bar = new Bar();

    foo.MyBar = bar;
    bar.MyFoo = foo;
}

Well done for figuring out where the original point of confusion was. — Andrew Shepherd, Jan 23 '18 at 00:08

score 8 · Answer 2 · answered Jul 08 '19 at 02:20

I also encountered this problem: Visual Studio just quietly stopped the test run with inconclusive result and it did not pinpoint what caused the problem. It just stopped the tests with blue icon indicating inconclusive result. In the Output window I noticed the same error message:

The active test run was aborted. Reason: Process is terminated due to StackOverflowException.

The solution was to run the test as "Debug Selected Test". Visual Studio then highlighted one of the lines participated in circular reference loop. One should place a break-point on that line and Debug the test once again. From this point debugger will step though the circular reference path.

StackOverflow in .NET unit testing when references are circular

2 Answers2

Linked