Hit the same issue as you – my test was passing everywhere, except for under NCrunch (could be any other instrumentation in your case). Hm. Debugging with SOS revealed additional roots held on a call stack of a test method. My guess is that they were a result of code instrumentation that disabled any compiler optimizations, including those that correctly compute object reachability.
The cure here is quite simple – don’t ever hold strong references from a method that does GC and tests for aliveness. This can be easily achieved with a trivial helper method. The change below made your test case pass with NCrunch, where it was originally failing.
[TestMethod]
public void WeakReferenceTest2()
{
var wRef2 = CallInItsOwnScope(() =>
{
var obj = new object();
var wRef = new WeakReference(obj);
wRef.IsAlive.Should().BeTrue(); //passes
GC.Collect();
wRef.IsAlive.Should().BeTrue(); //passes
return wRef;
});
GC.Collect();
wRef2.IsAlive.Should().BeFalse(); //used to fail, now passes
}
private T CallInItsOwnScope<T>(Func<T> getter)
{
return getter();
}