ILGPU v2.0: New Test Environment

[m4rs-mt]

Adds the complete test suite that exercises every stage of the new AOT compiler pipeline: from IR emission and backend codegen through to actually launching kernels on CPU/GPU. Replaces the retired legacy ILGPU.Tests, ILGPU.Tests.CPU, ILGPU.Tests.Cuda, and ILGPU.Algorithms.Tests projects with a single, layered suite aimed at the new compiler.

Also registers the Snapshots submodule that backs the IR snapshot tests, and ships a regeneration helper for updating those golden files. See ILGPU-Snapshots for more information.

The first commit is a PR placeholder for the runtime-library, AOT-compiler, compiler-bindings, and AI-readiness PRs; once those changes land on master they collapse into real merge commits.

A note on authorship - AI warning

Much of the test-infrastructure work in this PR was done with AI-assistant pair programming (Claude via Claude Code). Commits that genuinely reflect this shared authorship — the test framework itself, the Snapshots submodule registration, and the snapshot-regeneration helper script - carry a Co-Authored-By: Claude trailer so the credit is explicit.

What's in this PR

Test suite structure (Src/ILGPUC.Tests/, 309 files)

• Framework (18 files) — TestBase, MsBuildRunner for subprocess builds, IntegrationProjectFixture to materialize fixture projects on disk, CompilerManagerFactory with per-backend env-var routing, KernelRegistry/KernelDiscovery, Availability / backend-probe gating, ExecutionTestBase, and a subprocess output harness.
• Kernels (35 files) — representative kernels used as compilation fixtures across the suite (basic arithmetic, compare, convert, control flow, loops, lambdas, calls, arrays/views, memory buffers, shared memory, atomics, bitwise, warp/group/grid, reduce/scan/radix-sort, structures, enums, value tuples, interop).
• IR snapshot tests (34 files) — compare emitted IR against golden .il fixtures provided by the Snapshots submodule. Covers every kernel family plus the pipeline-stage comparison harness.
• Backend coverage tests (5 files) — cross-backend codegen coverage across CPU/CUDA/Metal/OpenCL/ROCm.
• Non-kernel tests (6 files) — compiler-utility, IR transformation, and type-system tests.
• Execution tests (38 files) — invoke each backend's native toolchain, load the resulting kernel binary, and verify the runtime output matches expectations.
• Test programs (157 files) — the actual kernel samples used by IR and execution tests, organized by feature (if, loop, switch, jump, phi, call, lambda, binary/unary int op, compare int/float, convert int/float, reinterpret-cast, enum, structure, value tuple, fixed buffers, array/view, local array, memory buffer, shared memory, atomics, warp, group, grid, and the runtime variants of reduce/scan/radix-sort).
• Integration tests (2 files) — MSBuild happy-path, multi-kernel, backend override, compile-error, incremental, and clean scenarios; NuGet pack/restore smoke test.
• Integration-project templates (11 files) — the tiny .csproj fixtures the integration tests consume.
• tests.md — describes the suite structure for contributors.

Snapshots submodule

Src/ILGPUC.Tests/Snapshots/ is registered as a submodule (.gitmodules added) providing the golden .il fixtures for the IR snapshot tests. Keeping them in a separate repo avoids bloating history with regeneration noise.

Snapshot-regeneration helper

Src/scripts/update-snapshots.sh — runs the IR test suite with ILGPU_UPDATE_IR=1, stages the resulting .il changes inside the submodule, and commits them.

Solution update

Src/ILGPU.sln registers the new ILGPUC.Tests project as the final commit.

CI coupling

The canonical .github/workflows/ci.yml was redesigned in the previous PR (new_ai_readiness) to include a build + tests + GPU Docker-run pipeline. This PR's final state matches that workflow expectation, so no workflow changes are needed here.

Scope boundary

No Docker, no CI workflow changes, no samples, no compiler-source changes.

Depends on

PR #1578.

Fixes

Closes #1249

Testing

Test runs

• dotnet build Src/ILGPU.sln - builds cleanly on the tip of this PR.
• dotnet test Src/ILGPUC.Tests/ILGPUC.Tests.csproj --blame-hang-timeout 360s