docs: add test migration TODO with 5-phase plan

- Phase 1: Remove duplicate old tests (6 files)
- Phase 2: Migrate remaining 7 old test files to new structure
- Phase 3: Create integration tests
- Phase 4: Clean up and verify
- Phase 5: Advanced improvements (slow markers, hypothesis, CI)
- Total: from 230 flat tests → ~240 organized tests in 3 directories

docs/test-migration-todo.md

@@ -0,0 +1,155 @@
+---
+title: "Test Migration TODO — From Flat to Structured Suite"
+date: 2026-05-15
+tags:
+  - testing/todo
+  - testing/migration
+status: active
+aliases: [test migration, test reorganization]
+related_notes:
+  - test-architecture
+---
+
+# Test Migration TODO
+
+> [!info] Current state
+> - **Old tests**: 230 tests in `tests/*.py` (flat structure)
+> - **New tests**: 94 tests in `tests/{physics,quality,common}/` (structured)
+> - **New tests already passing**: ✅ 94/94
+> - **Old tests still passing**: need to verify after removing duplicates
+
+## Phase 1: Remove duplicate old tests (P0 — blocking)
+
+The old files in `tests/` root contain tests that are now covered by the new structure. Remove them:
+
+- [ ] **1.1** Remove `tests/test_fermi.py` — covered by `tests/physics/test_fermi.py` + `tests/quality/test_api_fermi.py`
+- [ ] **1.2** Remove `tests/test_finite_size.py` — covered by `tests/physics/test_finite_size.py` + `tests/quality/test_api_finite_size.py`
+- [ ] **1.3** Remove `tests/test_screening.py` — covered by `tests/physics/test_screening.py` + `tests/quality/test_api_screening.py`
+- [ ] **1.4** Remove `tests/test_exchange.py` — covered by `tests/physics/test_exchange.py` + `tests/quality/test_api_exchange.py`
+- [ ] **1.5** Remove `tests/test_radiative.py` — covered by `tests/physics/test_radiative.py` + `tests/quality/test_api_radiative.py`
+- [ ] **1.6** Remove `tests/test_phase_space.py` — covered by `tests/physics/test_phase_space.py` + `tests/quality/test_api_phase_space.py`
+
+**After removal**: ~136 old tests remain (fitter, spectrum, detector, cw_extractor, multi_branch, nuclear_data, logging).
+
+## Phase 2: Migrate remaining old tests (P1 — high priority)
+
+Move the remaining old tests to the new structure:
+
+### 2.1 Integration tests → `tests/integration/`
+- [ ] **2.1.1** `tests/test_spectrum.py` → `tests/integration/test_spectrum_pipeline.py`
+  - Full pipeline tests (from_config → evaluate → components)
+  - Declarative detector response tests
+  - These are integration tests, not component tests
+
+### 2.2 Physics tests → `tests/physics/`
+- [ ] **2.2.1** `tests/test_detector_response.py` → `tests/physics/test_detector_response.py`
+  - 23 tests — physics behavior (normalization, resolution, convolution)
+  - Split into: `test_detector_response.py` (physics) + `tests/quality/test_api_detector_response.py` (API)
+
+- [ ] **2.2.2** `tests/test_fitter.py` → `tests/physics/test_fitter.py`
+  - 16 tests — fit quality, covariance, confidence intervals
+  - Split: physics (fit quality) + quality (API)
+
+- [ ] **2.2.3** `tests/test_cw_extractor.py` → `tests/physics/test_cw_extractor.py`
+  - 18 tests — shape factor extraction accuracy
+  - Split: physics (extraction) + quality (API)
+
+- [ ] **2.2.4** `tests/test_multi_branch.py` → `tests/physics/test_multi_branch.py`
+  - 26 tests — multi-branch physics
+  - Split: physics (branching) + quality (API)
+
+- [ ] **2.2.5** `tests/test_nuclear_data.py` → `tests/quality/test_nuclear_data.py`
+  - 21 tests — mostly API/parsing tests
+  - These are quality tests (input validation, parsing)
+
+### 2.3 Quality tests → `tests/quality/`
+- [ ] **2.3.1** `tests/test_logging_utils.py` → `tests/quality/test_logging_utils.py`
+  - 23 tests — all API tests (no physics)
+  - Direct move, no splitting needed
+
+## Phase 3: Create shared integration test (P2)
+- [ ] **3.1** Create `tests/integration/test_full_pipeline.py`
+  - End-to-end: config → spectrum → convolve → export → reimport
+  - Multi-branch → weighted sum → export
+  - Verify CSV export matches reimport
+
+## Phase 4: Clean up (P3)
+- [ ] **4.1** Remove old `tests/test_*.py` files that were migrated
+- [ ] **4.2** Verify all tests pass: `python3 -m pytest tests/ -v`
+- [ ] **4.3** Verify test count matches expected: ~136 (was 230, removed ~94 duplicates)
+- [ ] **4.4** Update `docs/test-architecture.md` with final structure
+- [ ] **4.5** Add `.gitkeep` to `tests/common/`, `tests/integration/` directories
+
+## Phase 5: Advanced improvements (P4 — nice to have)
+- [ ] **5.1** Add `pytest.mark.slow` to long-running tests
+- [ ] **5.2** Add `pytest.mark.requires_ensdf` to tests needing paceENSDF
+- [ ] **5.3** Consider adding `hypothesis` for property-based testing of edge cases
+- [ ] **5.4** Add `pytest-timeout` to prevent hangs
+- [ ] **5.5** Add CI badge for test status
+
+## Files to create/modify
+
+### New files (already created)
+- ✅ `tests/common/__init__.py`
+- ✅ `tests/common/test_property_tests.py` — shared property helpers
+- ✅ `tests/common/test_api_tests.py` — shared API helpers
+- ✅ `tests/physics/test_fermi.py`
+- ✅ `tests/physics/test_phase_space.py`
+- ✅ `tests/physics/test_finite_size.py`
+- ✅ `tests/physics/test_screening.py`
+- ✅ `tests/physics/test_exchange.py`
+- ✅ `tests/physics/test_radiative.py`
+- ✅ `tests/quality/test_api_fermi.py`
+- ✅ `tests/quality/test_api_phase_space.py`
+- ✅ `tests/quality/test_api_finite_size.py`
+- ✅ `tests/quality/test_api_screening.py`
+- ✅ `tests/quality/test_api_exchange.py`
+- ✅ `tests/quality/test_api_radiative.py`
+
+### Files to create (remaining)
+- `tests/integration/test_spectrum_pipeline.py`
+- `tests/integration/test_full_pipeline.py`
+- `tests/physics/test_detector_response.py`
+- `tests/quality/test_api_detector_response.py`
+- `tests/physics/test_fitter.py`
+- `tests/quality/test_api_fitter.py`
+- `tests/physics/test_cw_extractor.py`
+- `tests/quality/test_api_cw_extractor.py`
+- `tests/physics/test_multi_branch.py`
+- `tests/quality/test_api_multi_branch.py`
+- `tests/quality/test_nuclear_data.py`
+- `tests/quality/test_logging_utils.py`
+
+### Files to delete
+- `tests/test_fermi.py`
+- `tests/test_finite_size.py`
+- `tests/test_screening.py`
+- `tests/test_exchange.py`
+- `tests/test_radiative.py`
+- `tests/test_phase_space.py`
+- `tests/test_spectrum.py`
+- `tests/test_detector_response.py`
+- `tests/test_fitter.py`
+- `tests/test_cw_extractor.py`
+- `tests/test_multi_branch.py`
+- `tests/test_nuclear_data.py`
+- `tests/test_logging_utils.py`
+
+## Test count comparison
+
+| Category | Before | After (target) |
+|---|---|---|
+| Common helpers | 0 | ~12 (shared, not counted) |
+| Physics tests | ~151 | ~151 (same, reorganized) |
+| Quality/API tests | ~79 | ~79 (same, reorganized) |
+| Integration tests | ~0 | ~10 (new) |
+| **Total unique tests** | **230** | **~240** |
+
+The duplicate tests (positivity, shape, NaN across 6 components = ~18 tests) are now covered by shared helpers, so the **effective test count decreases** while coverage stays the same or improves.
+
+## References
+
+- [pytest markers documentation](https://docs.pytest.org/en/stable/how-to/mark.html)
+- [pytest test collection](https://docs.pytest.org/en/stable/explanation/goodpractices.html#test-collection)
+- [NumPy testing guidelines](https://numpy.org/doc/stable/reference/testing.html)
+- [Property-based testing with Hypothesis](https://hypothesis.readthedocs.io/)