CSHARP-5840: Proper XUnit shared test fixture for Atlas tests

[ajcvickers]

Replaces the suite's dependence on pre-configured Atlas sample databases and search indexes. The new AtlasSearchFixture (collection-scoped) owns a single client, an EventCapturer, and a fixture-managed atlas_search_ database. Lazy seeders populate historical_documents, movies, embedded_movies, airbnb_listings, test_classes, binary_vector_items, auto_embed_movies, two synonym source collections, and the existing return-scope directors collection, and create the ten search/vector indexes required by the tests (waiting for READY). Dispose drops the whole database.

The seed data is baked in as C# literals in AtlasSearchFixtureSeedData.cs (generated by tests/Tools/AtlasSeedExtractor from Atlas Local sample data once) so the test suite has zero runtime dependency on sample databases — only on an Atlas-search-capable cluster being reachable at ATLAS_SEARCH_URI. Embeddings are preserved as real Voyage-AI float32 vectors via BinaryVectorFloat32.

AtlasSearchTests, VectorSearchTests, AutoEmbedVectorSearchTests, and AtlasSearchIndexManagementTests join via [Collection(AtlasSearchCollection.Name)] and pull their client / collections through the fixture. AtlasSearchTests loses its static __indexesCreated / __databaseUniquifier / __returnScopeTestCount machinery and the inline return-scope seed. AtlasSearchTestsUtils is obsoleted.

AutoEmbedVectorSearchTests now run for real (the previous CSHARP-5840 skip is gone): the auto-embed collection and index live in the fixture so the Voyage AI embedding work happens once per test session instead of three times, the corpus is reduced to 4 movies (2 pass the runtime+year filter, 2 don't), and the ctor's unbounded wait loop is replaced with a 15-minute deadline that surfaces a clear error mentioning VOYAGE_API_KEY. Gated on a new AUTO_EMBEDDING_TESTS_ENABLED env var so contributors without a Voyage AI key can still run the rest of the Atlas Search suite. When enabled, the Atlas Local container must have VOYAGE_API_KEY provisioned via the Atlas UI's Model API Keys page (the key must authenticate against ai.mongodb.com, not api.voyageai.com). docker-compose.atlas-local.yml is included as a convenience launcher.

Count- and ranking-dependent assertions are recalibrated for the lean corpus: phrase-match counts drop from 108 to 1, geo-result counts from 25 to membership checks, and vector-search top-K assertions switch from order-sensitive ShouldBeEquivalentTo to order-insensitive BeEquivalentTo. The Pinocchio→Oz swap in VectorSearch top-5 is documented in the test where it lives. The Rerank test guards on AtlasSearchFixture.IsRerankSupported, which probes the deployment on first use.

Validated against Atlas Local: 77/77 AtlasSearch* tests pass, 36/36 AtlasSearchIndexManagement tests pass, 3/3 AutoEmbedVectorSearchTests pass (with a valid VOYAGE_API_KEY), 74 tests skip cleanly when env vars are unset, and no atlas_search_* databases remain after the suite exits.

[Copilot]

Pull request overview

This PR refactors the Atlas Search integration test suite to use a collection-scoped xUnit fixture that provisions its own ephemeral database, seed data, and required Atlas Search/vector indexes, eliminating reliance on pre-populated sample databases.

Changes:

• Add AtlasSearchFixture + AtlasSearchCollection to centralize client/event capture and lazily seed collections/indexes for Atlas Search tests.
• Update Atlas Search, Vector Search, Auto-embed Vector Search, and index-management tests to consume seeded collections via the fixture and adjust assertions for the reduced deterministic corpus.
• Add a one-shot AtlasSeedExtractor tool and a convenience docker-compose.atlas-local.yml for running Atlas Local with Voyage AI auto-embedding.

Reviewed changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tests/Tools/AtlasSeedExtractor/README.md	Documents the seed-extraction tool used to generate embedded C# seed literals.
tests/Tools/AtlasSeedExtractor/Program.cs	Implements deterministic extraction + C# emission of curated sample documents/embeddings.
tests/Tools/AtlasSeedExtractor/AtlasSeedExtractor.csproj	Adds the new tool project targeting net10.0.
tests/MongoDB.Driver.Tests/Search/VectorSearchTests.cs	Switches tests to fixture-provided client/collections and updates ranking assertions for lean seed.
tests/MongoDB.Driver.Tests/Search/AutoEmbedVectorSearchTests.cs	Enables real auto-embed tests behind env var gating and uses fixture-owned corpus/index.
tests/MongoDB.Driver.Tests/Search/AtlasSearchTestsUtils.cs	Removes the old ad-hoc Atlas Search client helper.
tests/MongoDB.Driver.Tests/Search/AtlasSearchTests.cs	Migrates to fixture-backed seeded collections/indexes and recalibrates corpus-dependent assertions.
tests/MongoDB.Driver.Tests/Search/AtlasSearchIndexManagmentTests.cs	Migrates index-helper tests to fixture-owned client and updates auto-embed gating/expectations.
tests/MongoDB.Driver.Tests/Search/AtlasSearchFixture.cs	Introduces the shared fixture that seeds collections and waits for indexes to become READY.
tests/MongoDB.Driver.Tests/Search/AtlasSearchCollection.cs	Adds the xUnit collection definition binding the fixture to test classes.
docker-compose.atlas-local.yml	Adds an Atlas Local compose file configured for Voyage AI auto-embedding.

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[sanych-sun]

I do agree that this tool looks useful, but do we really need it in the Driver's repo? Are we expecting to use it frequently?

Should we have a separate repo for tools like this? Somewhere under https://github.com/mongodb-labs .

I'm not insisting, just asking.

[ajcvickers]

I'll just remove it.

[sanych-sun]

LGTM