Generates C# backend unit and integration tests for EF Core DbContext repositories, domain services, and vertical slice handlers using xUnit or NUnit against SQLite in-memory or Testcontainers databases, one test per scenario and business rule, each tagged with [UseCase]. Use when the user asks to "write backend tests for C#", "write .NET tests for this handler", "test ef core context", "write integration tests for dotnet", or mentions xUnit or NUnit handler tests. Blazor component tests are /bunit-test, browser tests /playwright-test.