//dot net digest: MSTest on Native AOT, unions in System.Text.Json, C# 15, Rider 2026.3

Seven .NET links of the week: MSTest 4.4 runs tests as Native AOT executables, Andrew Lock on serializing unions and closed hierarchies with System.Text.Json, C# 15 features, Rider 2026.3 EAP 1, extension-member properties, September servicing with 8 CVEs, .NET Conf 2026 Community Days CFP.