Inexplicable Guid values

So I have this fake object definition (), that has a fake method in it :

IFooRepositoryClass fooRepo = A.Fake<IFooRepositoryClass>();

A.CallTo(() => fooRepo.FooFunctionAsync(A<Guid>.Ignored).ReturnsLazily(
    (Guid fooId) => {
        fooInternalObject.DoSomething(fooId);
    }
);

As you can see, thing out of the ordinary.

Later, in my XUnit tests, I call the fake function :

Guid testGuid = new Guid("aaaaaaaa-9a88-4746-914b-aaaaaaaaaaaa"); //I changed to "aaaaa" to make it easily recognizable
await fooRepo.FooFunctionAsync(testGuid).configureAwait(false);

I put a breakpoint on that instruction : await fooRepo.FooFunctionAsync(testGuid).configureAwait(false); …I see that testGuid is indeed aaaaaaaa-9a88-4746-914b-aaaaaaaaaaaa

But then I put a breakpoint inside, on this instruction : fooInternalObject.DoSomething(fooId);

To my great surprise, fooId has a weird value with lots of zeros, different at each run! f933b838-007b-0000-0000-000000000000 785bb288-001a-0000-0000-000000000000 4d4bb8d8-0012-0000-0000-000000000000 etc.

What the hell is going on?

Even weirder : I shared my branch to a colleague. He has the exact same code as me. …But for him, fooId has the expected value, i.e. the value of testGuid! He shared his screen, I shared mine. Everything condition seems identical. Only the Guid differs : Expected value for him, bogus values for me. I cleaned the solution, rebuilt, even restarted VS. to no avail!

What the hell is going on? x2

I’m not expecting anyone to fix my unit tests, but maybe this is a well-known behaviour under certain conditions. Ever seen that? Especially those weird 000000 Guid values?

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cross-posted to StackOverflow

[thomaslevesque]

I don’t think that’s possible. I guess it would be possible in a language like C, but C# has strong typing enforced by the runtime. A DateTime can’t accidentally be interpreted as a GUID…

[jeancallisti]

The mystery remains. I guess we’ll never know!