⭐ Testing

Framework: MSTest.Sdk on .NET's newer Microsoft.Testing.Platform (MTP) runner — already pinned in global.json from the original SDK research, not a new choice. MTP is a genuinely different CLI surface from the older VSTest-based dotnet test (its own --help says so directly) — coverage and TRX reporting are both built into the runner itself, confirmed against a real scratch project rather than assumed.

Testing is no longer a separate end-of-migration phase. tests/eShop.ServiceDefaults.UnitTests — the first real test project, and now the first to reach full coverage: all 7 source files, 33 passing tests — was added and grown before the source migration resumed past IntegrationEventLogEF. Going forward, every project gets its own test project in the same unit of work as its source files — src/Shared/ included, despite not being a .csproj project itself.

Two patterns worth knowing:

• InternalsVisibleTo for internal classes worth testing directly, rather than reflection (brittle) or skipping coverage — used on OpenApiOptionsExtensions, which is internal end-to-end.
• NSubstitute (already centrally pinned, upstream's own Ordering.UnitTests uses it too) for behavior only reachable through a DI/HTTP pipeline — HttpClientExtensions's bearer-token-injecting handler is a private nested class, only exercisable through its public AddAuthToken surface plus a mocked IAuthenticationService.

Tracked, not solved: wanted one combined HTML report across every test project; MTP's --report-html produces one file per project instead (confirmed via a real 2-project scratch solution). The real fix (microsoft/testfx#10529) merged 2026-08-09 but hasn't shipped in a NuGet release yet — Dependabot already tracks the package individually, so no new tooling is needed to know when it does.

Full detail in todo.md's "Testing strategy" section and docs/architecturedesign.md Section 11.