Add docs-tests.yml; remove test_doc_snippets.py from rust-test.yml

.github/workflows/docs-tests.yml

@@ -0,0 +1,62 @@
+name: Documentation Tests
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'docs/**'
+      - 'diff_diff/**'
+      - 'tests/test_doc_snippets.py'
+      # tests/conftest.py is auto-loaded by pytest for the snippet
+      # test run and mutates sys.path + MPLBACKEND (conftest.py:14, 18);
+      # changes there can break snippet exec without touching the test
+      # file itself.
+      - 'tests/conftest.py'
+      - 'pyproject.toml'
+      - '.github/workflows/docs-tests.yml'
+  pull_request:
+    branches: [main]
+    types: [opened, synchronize, reopened, labeled, unlabeled]
+    paths:
+      - 'docs/**'
+      - 'diff_diff/**'
+      - 'tests/test_doc_snippets.py'
+      - 'tests/conftest.py'
+      - 'pyproject.toml'
+      - '.github/workflows/docs-tests.yml'
+  schedule:
+    # Weekly Sunday 6am UTC - smoke test that snippets still execute
+    # against current upstream deps (mirrors notebooks.yml schedule).
+    - cron: '0 6 * * 0'
+
+permissions:
+  contents: read
+
+jobs:
+  doc-snippets:
+    name: Validate RST code snippets
+    if: >-
+      github.event_name != 'pull_request'
+      || contains(github.event.pull_request.labels.*.name, 'ready-for-ci')
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Set up Python
+        uses: actions/setup-python@v6
+        with:
+          # 3.14 to mirror Pure Python Fallback (the only existing job
+          # that actually ran these tests). notebooks.yml uses 3.11 for
+          # nbmake compat, not relevant here.
+          python-version: '3.14'
+
+      - name: Install dependencies
+        # Keep in sync with pyproject.toml [project.dependencies] and [project.optional-dependencies.dev]
+        run: pip install numpy pandas scipy pytest
+
+      - name: Run doc snippet tests in pure Python mode
+        # PYTHONPATH=. lets the test import diff_diff directly from
+        # source without invoking the maturin/Rust build (mirrors Pure
+        # Python Fallback at rust-test.yml:189-193).
+        run: PYTHONPATH=. DIFF_DIFF_BACKEND=python pytest tests/test_doc_snippets.py -v

.github/workflows/rust-test.yml

@@ -7,6 +7,9 @@ on:
       - 'rust/**'
       - 'diff_diff/**'
       - 'tests/**'
+      # tests/test_doc_snippets.py is owned by docs-tests.yml; exclude it
+      # so a harness-only edit does not fan out into the Rust matrix.
+      - '!tests/test_doc_snippets.py'
       - 'pyproject.toml'
       - '.github/workflows/rust-test.yml'
   pull_request:
@@ -16,6 +19,7 @@ on:
       - 'rust/**'
       - 'diff_diff/**'
       - 'tests/**'
+      - '!tests/test_doc_snippets.py'
       - 'pyproject.toml'
       - '.github/workflows/rust-test.yml'
 
@@ -155,14 +159,18 @@ jobs:
       - name: Run tests with Rust backend (Unix)
         if: runner.os != 'Windows'
         working-directory: /tmp
-        run: DIFF_DIFF_BACKEND=rust pytest tests/ -q -n auto --dist worksteal -m ''
+        # Doc snippet tests own .github/workflows/docs-tests.yml; ignore
+        # them here to keep one workflow per surface and avoid double
+        # execution (the matrix copies tests/ to /tmp/tests without
+        # docs/, so this ignore is defensive on the Rust path).
+        run: DIFF_DIFF_BACKEND=rust pytest tests/ --ignore=tests/test_doc_snippets.py -q -n auto --dist worksteal -m ''
 
       - name: Run tests with Rust backend (Windows)
         if: runner.os == 'Windows'
         working-directory: ${{ runner.temp }}
         run: |
           $env:DIFF_DIFF_BACKEND="rust"
-          pytest tests/ -q -n auto --dist worksteal -m ''
+          pytest tests/ --ignore=tests/test_doc_snippets.py -q -n auto --dist worksteal -m ''
         shell: pwsh
 
   # Test pure Python fallback (without Rust extension)
@@ -190,4 +198,8 @@ jobs:
           PYTHONPATH=. python -c "from diff_diff import HAS_RUST_BACKEND; print(f'HAS_RUST_BACKEND: {HAS_RUST_BACKEND}'); assert not HAS_RUST_BACKEND"
 
       - name: Run tests in pure Python mode
-        run: PYTHONPATH=. DIFF_DIFF_BACKEND=python pytest tests/ -q --ignore=tests/test_rust_backend.py -n auto --dist worksteal
+        # Doc snippet tests own .github/workflows/docs-tests.yml; ignore
+        # them here to keep one workflow per surface (this is the only
+        # invocation that actually executes test_doc_snippets.py since
+        # this job runs from the repo root, not /tmp/tests).
+        run: PYTHONPATH=. DIFF_DIFF_BACKEND=python pytest tests/ -q --ignore=tests/test_rust_backend.py --ignore=tests/test_doc_snippets.py -n auto --dist worksteal

TODO.md

@@ -120,7 +120,7 @@ Deferred items from PR reviews that were not addressed before merge.
 |-------|----------|----|----------|
 | ImputationDiD event-study SEs recompute full conservative variance per horizon (should cache A0/A1 factorization) | `imputation.py` | #141 | Low |
 | Rust faer SVD ndarray-to-faer conversion overhead (minimal vs SVD cost) | `rust/src/linalg.rs:67` | #115 | Low |
-| Unrelated label events (e.g., adding `bug` label) re-trigger CI workflows when `ready-for-ci` is already present; filter `labeled`/`unlabeled` events to only `ready-for-ci` transitions | `.github/workflows/rust-test.yml`, `notebooks.yml` | #269 | Low |
+| Unrelated label events (e.g., adding `bug` label) re-trigger CI workflows when `ready-for-ci` is already present; filter `labeled`/`unlabeled` events to only `ready-for-ci` transitions | `.github/workflows/rust-test.yml`, `notebooks.yml`, `docs-tests.yml` | #269 | Low |
 | `bread_inv` as a performance kwarg on `compute_robust_vcov` to avoid re-inverting `(X'WX)` when the caller already has it. Deferred from Phase 1a for scope. HC2 and HC2+BM both need the bread inverse, so a shared hint would save one `np.linalg.solve` per sandwich. | `linalg.py::compute_robust_vcov` | Phase 1a | Low |
 | Rust-backend HC2 implementation. Current Rust path only supports HC1; HC2 and CR2 Bell-McCaffrey fall through to the NumPy backend. For large-n fits this is noticeable. | `rust/src/linalg.rs` | Phase 1a | Low |
 | CR2 Bell-McCaffrey DOF uses a naive `O(n² k)` per-coefficient loop over cluster pairs. Pustejovsky-Tipton (2018) Appendix B has a scores-based formulation that avoids the full `n × n` `M` matrix. Switch when a user hits a large-`n` cluster-robust design. | `linalg.py::_compute_cr2_bm` | Phase 1a | Low |