chore(tests): upgrade NUnit 3 to 4.6.1 across all test projects

[ottobolyos]

Summary

Upgrade every test project from NUnit 3.14.0 to NUnit 4.6.1 — the current stable line — and normalize the fragmented NUnit / NUnit3TestAdapter versions across the test tree that had drifted onto two different baselines.

Motivation

NUnit 3's lifetime is now maintenance-only; NUnit 4 is the active stable line and receives new features, .NET 8/9 hardening, and framework-level fixes. Four of the nine test csprojs still sat on NUnit 3.13.3 with NUnit3TestAdapter 4.3.1/4.5.0, while the other five had already moved to 3.14.0 + 4.6.0 — a fragmented baseline that risked masking version-specific behavior. Bringing everything onto NUnit 4.6.1 clears the drift, aligns the runner surface (relevant for the upcoming Stryker.NET adoption in a follow-up PR), and gets ahead of NUnit 3's deprecation curve.

Approach

Two commits, in the shape [normalize] then [bump]:

1. chore(tests): normalize NUnit and NUnit3TestAdapter versions across tests — mechanical version alignment across the four lagging csprojs (MTConnect-Compliance-Tests, MTConnect.NET-AgentModule-MqttRelay-Tests, MTConnect.NET-JSON-Tests, MTConnect.NET-JSON-cppagent-Tests) so all nine sit on the highest currently-in-use pair before the framework bump. Zero source changes; behavior identical.

2. chore(tests): upgrade NUnit 3.14.0 to 4.6.1 across all test projects — every test csproj moves to NUnit 4.6.1, and two compiler-driven source migrations follow:

   • CS0121 delegate-overload ambiguity (84 sites, 20 files). NUnit 4 added Action / Func<T> overloads alongside the legacy TestDelegate / ActualValueDelegate overloads on Assert.DoesNotThrow, Assert.Throws<T>, Assert.ThrowsAsync<T>, Assert.Multiple, and Assert.That. Lambda arguments are now ambiguous under overload resolution, so each affected site casts the lambda to (Action) to unambiguously bind to the new Action overload. Assert.That sites are cast only when the constraint is a Throws.* form (void-lambda variant); the value-returning Is.* form is not affected in this corpus. Where the (Action) cast introduced a bare Action reference in files that only transitively imported System, using System; was added.

   • CS9202 Assert.AreEqual extension-method dispatch (3 sites, 2 files). NUnit 4 removed the classic static Assert.AreEqual and replaced it with an extension-method shim on Assert exposed by NUnit.Framework.Legacy. The extension-method shim requires C# 14 (feature extensions), which the test projects do not target. The safe migration is ClassicAssert.AreEqual from NUnit.Framework.Legacy — a plain static method that works under every C# language version. Two files (AgentUuidDeterministicDefaultTests.cs, XmlStreamsResponseDocumentTests.cs) switch the callers and add using NUnit.Framework.Legacy;.

NUnit3TestAdapter stays at 4.6.0 — the adapter version tracks the adapter's own release line, not the framework version, and 4.6.0 supports both NUnit 3 and NUnit 4 discovery.

Depends on

(no in-flight PR dependencies — merges cleanly against master.)

Dime review cycle 1

Six-agent sweep (code-review, security-audit, simplification, improvement, documentation-audit, test-coverage-audit) at head 3a8954cd. All MEDIUM+ findings closed atomically or tracked with an issue number.

Atomic fix landed on 5e205e3a — swap the 3 ClassicAssert.AreEqual sites to Assert.That(actual, Is.EqualTo(expected)) and drop both using NUnit.Framework.Legacy; imports:

• [F-CR-001] MEDIUM (code-review) — same recommendation.
• [F-IMP-002] MEDIUM (improvement) — same recommendation.
• [F-SIMP-001] LOW (simplification, AgentUuidDeterministicDefaultTests.cs) — same recommendation.
• [F-SIMP-002] LOW (simplification, XmlStreamsResponseDocumentTests.cs) — same recommendation.

Four agents converged on the same fix — ClassicAssert.AreEqual is NUnit's own "temporary expedience", constraint-based Assert.That reads uniformly with every other assertion in the diff, and the Legacy import is no longer needed. Full-solution build stays at 0 warnings, 0 errors; the two focused suites (AgentUuidDeterministic*, XmlStreamsResponseDocument*) stay green after the swap.

MEDIUM tracked via new issue #240:

• [F-IMP-001] MEDIUM (improvement) — adopt Directory.Packages.props (Central Package Management). All 9 test csprojs now duplicate NUnit@4.6.1, NUnit3TestAdapter@4.6.0, Microsoft.NET.Test.Sdk@17.14.1, coverlet.collector@6.0.4 — the first drift will be silent (and chore(tests): upgrade NUnit 3 to 4.6.1 across all test projects #239 itself was born from precisely that pattern). Sequenced before the follow-up Stryker.NET adoption PR.

LOW SKIP-rationale — minimal-diff justifies the mechanical shape; constraint-model migration is legitimate follow-up scope:

• [F-CR-002] — convert 71 (Action)(() => …) casts on Assert.DoesNotThrow / Throws<T> / That(delegate, Throws.…) to Assert.That(() => …, Throws.Nothing) / Throws.TypeOf<T>().
• [F-CR-004] — same tradeoff on JsonSampleValueToObservationTests.cs and JsonSampleValueConverterEdgeCaseTests.cs.
• [F-IMP-003] — (Action) → (TestDelegate) sed sweep. Style call; either reads well.

LOW TRACK — follow-up-scoped, not blocking:

• [F-CR-003] — replace Assert.Multiple((Action)(() => { … })) blocks with using (Assert.EnterMultipleScope()) { … } (NUnit 4.2+). Cast-free and reads as ambient scope; will be flagged as a nice cleanup in a subsequent quality-pass PR.
• [F-IMP-004] — benchmark [assembly: Parallelizable(ParallelScope.Fixtures)] per test project; suites that bind to fixed HTTP/MQTT ports need per-project audit before flipping. Land under a dedicated performance chore.

CLOSE — confirmations only, no code change:

• [F-IMP-005] — Stryker.NET follow-up unblocked (no Assert.Throws weakening in diff).
• [F-SEC-001, F-SEC-002, F-SEC-003] — no CVE surface introduced; every Assert.Throws diff hunk preserves the lambda body verbatim; XmlReaderSettings note is pre-existing pattern outside PR scope.
• [F-TEST-001, F-TEST-002, F-TEST-003, F-TEST-004] — behavior parity spot-checked across all 20 files; Is.EquivalentTo sites stay on same-type collections; zero test smells introduced.
• [F-TEST-005] — Docs-Tests bluefin-flake escape hatch already exists (--filter "Category!=E2E"); RouteCheckHelpersTests.cs is deliberately Category-free and runs in either mode.

Documentation audit — CLEAN. No /// doc regression on the 25 touched .cs files; no stale NUnit 3 references in docs/**, root markdown, .github/workflows/*.yml, or CHANGELOG (none exists); MTConnect.NET-Tests-Agents (fixture-only, no NUnit ref) is not referenced anywhere that would become inconsistent.

Head after cycle 1: 5e205e3a6371feca93b9782e71dd4dce7d61bc79. Integration branch integration/up-to-pr-239 at cfbf89448e221233a157e4dd9098f22995d85fd7.