Create an analyzer to flag when a test case isn't serializable

[bradwilson]

In v2 and non-AOT v3, test cases must be serializable. There should be an analyzer to trigger when this isn't done.

Note that in v3, the test case might not be directly serializable, since serialization might be handled by an "external" serializer that implements IXunitSerializer rather than the test case itself implementing IXunitSerializable.

From #3528

[ana1250]

I'd like to take this on. I've been digging through the current SerializabilityAnalyzer and SerializableTypeSymbols to see how this fits in.

My plan is to add two new rules: X3004 (for sealed classes that definitely aren't serializable) and X3005 (a warning for unsealed classes, since a subclass or external serializer might handle it). It'll check for ITestCase across both v2 and v3, validating against IXunitSerializable, the [JsonTypeID] attribute, and the v3 external serializer registrations.

I also noticed a small typo in SerializabilityAnalyzer.cs (AnalayzeSerializability) that I'll clean up while I'm at it.

[bradwilson]

If you do this, please do it on the rel/2.0.0 branch, because the main branch is significantly out of date (for example, xUnit3004 and xUnit3005 area already taken) and there are no plans to release from the main branch until it has had rel/2.0.0 merged into it.

Thanks!

[ana1250]

Thanks for the headsup!
Right, I was checking the main hence found x3004 and x3005 available.
I went with x3006 and x3007.
Raised the PR as well.

[bradwilson]

Fix available in analyzers 2.0.0-pre.43 https://xunit.net/docs/using-ci-builds

[bradwilson]

Tag: @Youssef1313