request: Can we also add a test for double-disposing a scope? I think the existing logic in AssertionScope will catch this and fail but it would be good to have coverage for our desired behaviour to prevent accidental changes in the future.

related question: Should it fail if we dispose the same scope twice, or should the second be a no-op? I know CA2202 warns against disposing multiple times, but the docs there also mention

A correctly implemented Dispose method can be called multiple times without throwing an exception. However, this is not guaranteed

@stevenaw Good point!

I went for not throwing an error as multiple calls to Dispose should be safe as per the interface specification remarks.

If an object's Dispose method is called more than once, the object must ignore all calls after the first one. The object must not throw an exception if its Dispose method is called multiple times.

The CA2202 is deprecated and no longer in the latest analyzer nuget package.

Thanks! I had somehow glossed over the part of the documentation where it said the rule was deprecated.

question: Should we dispose of any open scopes here after reporting the error? I'm not sure if there could be any stability issues with leaving them around given they themselves contain a reference to a particular TestExecutionContext

We cannot as we don't have a reference to them. I don't think it is worth it to add them as references to the context.
Every test gets it own new context and the old scope and context will be garbage collected.

Ok sounds good. My thinking had indeed been probing if it made sense to track these on the context as a Stack<AssertionScope> instead of the MultipleAssertLevel counter, but as you say we can also fulfill the behaviour without doing those broader changes.