Many (almost all?) properties are expected to be added today to TestNode, while some of them feel to me they should belong to TestNodeUpdateMessage instead. Examples:

• TimingProperty
  • This doesn't feel like a property of TestNode itself, but rather a success/fail/error/timeout/cancel update message.
  • Fixed in Move some MTP properties from TestNode to TestNodeUpdateMessage #6124
• TestNodeStateProperty (and derived)
  • The name gives impression that it's property of the test node, but I also tend to think it belongs to TestNodeUpdateMessage. Take the case of folded tests in MSTest where we will report multiple results for the same TestNode. To me that's an indicator that the property belongs to the update message not the node itself.
• StandardOutputProperty/StandardErrorProperty
  • Fixed in Move some MTP properties from TestNode to TestNodeUpdateMessage #6124
• FileArtifactProperty
  • Fixed in Move some MTP properties from TestNode to TestNodeUpdateMessage #6124

On the other hand, the following properties are present on TestNode today and are correct:

• TestFileLocationProperty
• TestMethodIdentifierProperty
• TestMetadataProperty

In addition, we should also revise Trx-specific properties:

https://github.com/microsoft/testfx/blob/0e87d5aafb41692309b310704c6fa858b146919c/src/Platform/Microsoft.Testing.Extensions.TrxReport.Abstractions/TrxReportProperties.cs

• TrxExceptionProperty, likely needs to be moved to TestNodeUpdateMessage
• TrxFullyQualifiedTypeNameProperty good on TestNode.
• TrxMessagesProperty, likely needs to be moved to TestNodeUpdateMessage
• TrxCategoriesProperty good on TestNode