Add pin tests for gaps found in downstream usage

[jbtule]

Why

Auditing a large downstream consumer (a separate private solution) for how it uses ImpromptuInterface surfaced a few real API usage patterns that aren't exercised anywhere in this test suite. This PR adds pin tests for those specific gaps only; naming is intentionally generic (no downstream business terms).

Gaps covered

1. Impromptu.DynamicActLike(object, params Type[]) (the non-generic, runtime-Type overload) has no existing test coverage anywhere in the suite. Added a basic round-trip test plus a repeated-call test with the same runtime Type.
2. ActLike<IList<T>> (a generic BCL collection interface) proxied over an object that only implements the dynamic-dispatch protocol (TryGetMember/TryInvokeMember/TryGetIndex/TrySetIndex), simulating lazy-materialized proxies (e.g. Dynamitey.DynamicObjects.Lazy). Only a non-generic array/indexer case (IStringIntIndexer) was previously tested; this exercises Count, indexer get, Contains, Add, and GetEnumerator() all being synthesized by the proxy, plus confirms the lazy factory only runs once.
3. Combining a proxy interface with an empty marker/tag interface via the typeof(...) overload. DoubleInterfacetest (existing) only combines two interfaces that both declare members; this adds coverage for a marker interface with zero members.

Validation

dotnet test .\Tests\UnitTestImpromptuInterface\UnitTestImpromptuInterface.csproj -c Debug -f net8.0

All 207 tests pass (203 existing + 4 new).

[Copilot]

Copilot review overview

🟡 Changes recommended

Add PinTests.cs to the WASM test project so these tests run in the browser-WASM test leg.

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Review effort: Lite
Findings: 1

Open (1)

• Add PinTests.cs to the WASM test project · New

What changed in this PR

Adds four focused pin tests for runtime interface proxying, lazy dynamic collections, and marker-interface composition.

Changes:

• Tests runtime-Type DynamicActLike calls.
• Tests lazy dynamic IList<int> proxy behavior.
• Tests combining a proxy with an empty marker interface.

File	Description
Tests/​UnitTestImpromptuInterface/​PinTests.cs	Adds four targeted tests and supporting proxy types; the file is not yet included in the WASM test project.

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[jbtule]

That one is right, and it is fixed in a323270 — PinTests.cs is now linked into the wasm project, which takes that leg from 114 to 118 tests, all passing (bun runtests.mjs).

It belongs there rather than being excluded: the file pulls in neither Moq nor IronPython, which are the two documented reasons SingleMethodInvoke.cs and Linq.cs stay out. And it is worth having in particular, because GenericListInterfaceOverLazyDynamicTest is the only generic-collection-over-DynamicObject proxy case that leg gets — the comparable existing ones live in the excluded Linq.cs.

A cold review of the same commit turned up four other things, all in a323270 as well:

• DynamicActLikeWithRuntimeTypeRepeatedTest did not pin its own API. Replacing the whole entry point with public static dynamic DynamicActLike(object o, params Type[] t) => o; left it green, because reading .Name off the unwrapped ExpandoObject gives the same answer. It now asserts each result is a proxy, that they are distinct instances, and that they share a proxy type — the reuse its comment claimed and nothing checked. Re-ran that same mutation afterwards: it now fails both tests rather than one.
• Assert.AreEqual(1, tForwarder.FactoryCallCount) could not fail. The increment sat behind the fixture's own _target == null guard, so the count could never exceed 1 whatever the proxy did. The factory now counts its own calls, which pins the property worth pinning: the proxy does not re-materialize the target per member call.
• TrySetIndex was implemented in the fixture and reached by no test, though the description listed it. Now exercised through the synthesized IList<int> setter.
• Header comments addressed a reviewer of a proposal ("can live directly in Tests/…", "would go in Support/SupportDefinitions.cs") rather than describing the file; and the runtime-Type gap is the public static entry point, not the behaviour — no-opping ActLikeMaker.DynamicActLike turns 17 existing tests red.

207 on net8.0 and net10.0, 213 on net47, 118 on browser-wasm.