Skip tests even if SkipException is coming from within Assert.Throws

[fredrikhr]

Updated in #12 (comment)

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As described in xunit/xunit#1722 the Xunit.Sdk.ThrowsException that is thrown from a failed execution of Assert.Throws (and related) does not capture the exception actually thrown.

The thrown Exception message does however contain the string Actual: typeof(Xunit.SkipException) if a SkipException was thrown inside the action or function passed to Assert.Throws.

Although the solution to search the ThrowsException message for that string is far from elegant, it works and can be replaced when xunit/xunit#1722 has been fixed.

Fixes #10.

[AArnott]

@couven92 Thanks for contributing. It looks to me though that my fix for the xunit bug you mention is already completed and in the xunit 2.4 release available on NuGet. So can we rework this PR with the more elegant fix that you mention?

[fredrikhr]

@AArnott thanks for the tip. If have updated the code. It now checks whether the first element is Xunit.Sdk.ThrowsException and checks if the exception that directly follows is skippable.

I hope it's okay that I have used newer language features (i.e. a pattern-matching switch block)

I ran dotnet outdated to update the package references to newer versions.

[AArnott]

Thanks. Yes, it's fine to use newer C# features. I personally find this switch statement harder to read than a single if/else pair (I reserve switch statements to more than two cases), but it's not a big deal.
Thanks for your contribution.