chore: migrate tests to xunit v3

[jeremydmiller]

Builds on #576. The package swap itself is now a 4-line edit in Directory.Packages.props:

Package	From	To
xunit → xunit.v3	2.9.3	3.2.2
xunit.runner.visualstudio	3.0.0	3.1.5
Microsoft.NET.Test.Sdk	17.12.0	18.8.1

Staying on the VSTest bridge deliberately — dotnet test, the Nuke DotNetTest targets, and coverlet.collector all keep working untouched. Microsoft Testing Platform is a clean follow-up now that v3 is in.

Mechanical changes

• Xunit.Abstractions is gone; ITestOutputHelper moved into Xunit, already a global Using. 15 stray usings deleted, nothing else.
• DocSamples drops its test packages rather than migrating — zero [Fact]/[Theory] methods, holds compile-checked doc samples, and isn't in jasperfx.slnx or any Nuke target. xunit.v3 would also have forced OutputType=Exe onto a Microsoft.NET.Sdk.Web project for nothing.
• MethodCallTester borrowed Xunit.Sdk.ErrorMessage as a return type for its codegen probes via a stray using Xunit.Sdk. The tests only assert the inferred type identity, so any reference type does — replaced with a local one, dropping an accidental dependency on xunit internals.

Zero IAsyncLifetime implementations and zero IClassFixture/ICollectionFixture usages in the repo, so none of the usual v3 migration work applied.

Three real failures — none mechanical

All three are latent problems v2 happened to hide. Worth reviewing individually:

1. HasReferenceToJasperFxTool had no guard — this is a product bug, not a test bug.

It loads every referenced assembly and reads its attributes. v3 test projects are executables, so Assembly.GetEntryAssembly() is now the test assembly instead of testhost.exe, and the walk reached a project reference whose own dependency is missing from the output → FileNotFoundException straight out of host startup.

This affects real consumers today: any application whose assembly graph contains an unresolvable reference — an optional dependency never deployed, something trimmed — crashes identically. Detection is best-effort, so unloadable assemblies are now skipped.

2. SliceGroupTests self-stubs IProjectionStorage, which extends IAsyncDisposable, and left DisposeAsync throwing NotImplementedException. v2 never called it; v3 disposes test classes implementing IAsyncDisposable, so all 16 tests in the class failed in teardown. The stub belongs to the storage contract, not xunit lifecycle — now a no-op.

3. run_an_async_command_that_fails was passing on test ordering alone. It asserts on output captured via Console.SetOut, but CommandExecutor renders failures through Spectre's AnsiConsole, which caches the writer it binds to on first use, process-wide. Console.SetOut cannot redirect an already-pinned Spectre console. The sibling happy-path tests passed only because they use plain Console.WriteLine. Now binds AnsiConsole explicitly, so it no longer depends on order.

Dead CI config retired

FRAMEWORK bound to no Nuke parameter, and DISABLE_TEST_PARALLELIZATION was read by nothing — no test project, runner config, or build target. The two suites that genuinely must not run concurrently already declare it in code via [assembly: CollectionBehavior(CollectionBehavior.CollectionPerAssembly)], which v3 still honors, so serialization is enforced where it can't be silently dropped. CONFIGURATION stays — it does bind.

Verification

Test counts match the v2 baseline exactly on both frameworks — no discovery loss:

Suite	net9.0	net10.0
CoreTests	475	475
CodegenTests	419	419
CommandLineTests	295	295
EventTests	648	648
EventStoreTests	72	72
CodegenTests.FSharp	1	—

Stable over three consecutive full runs (the order/parallelism risk of a v3 swap). smoke-test-aot and smoke-test-commands also pass.

🤖 Generated with Claude Code