# Test — DetectionClasses (Load, Hotkeys, Click, Fallback)

**Task**: AZ-472_test_detection_classes
**Name**: DetectionClasses load + 1-9 hotkeys + click path + empty/5xx fallback
**Description**: Implement the 4 blackbox tests pinning `<DetectionClasses>` behavior: load from `/api/annotations/classes`, hotkey 1-9 → `classes[(key-1) + P]` (P = current PhotoMode offset), click-to-select path, and the fallback list when the API is empty or 5xx.
**Complexity**: 3 points
**Dependencies**: AZ-456_test_infrastructure
**Component**: 06_annotations (DetectionClasses) + 11_class-colors (Blackbox Tests)
**Tracker**: AZ-472
**Epic**: AZ-455

## Problem

`<DetectionClasses>` is keyboard-driven during annotation; the hotkey-to-class mapping changes with PhotoMode (offset P). Wrong P leaks the wrong class number on save — a quality regression hard to spot without explicit hotkey tests.

## Outcome

- 4 scenarios pass — load contract, hotkey arithmetic, click selection, fallback robustness.

## Scope

### Included

| Scenario | Profile | Source file |
|----------|---------|-------------|
| FT-P-44 — DetectionClasses loads from `/api/annotations/classes` | fast + e2e | blackbox-tests.md |
| FT-P-45 — class hotkey 1–9 selects `classes[(key-1) + P]` | fast | blackbox-tests.md |
| FT-P-46 — class click path | fast | blackbox-tests.md |
| FT-P-47 — fallback class list on API empty/5xx | fast | blackbox-tests.md |

### Excluded

- PhotoMode switching itself (covered in 18_test_photo_mode).
- Class CRUD via Admin (out of scope; per-feature task in Phase B).

## Acceptance Criteria

**AC-1: Load contract**
FT-P-44 — outbound URL is `/api/annotations/classes`; response shape matches `seed_classes` (per the contract).

**AC-2: Hotkey arithmetic**
FT-P-45 — for each PhotoMode P ∈ {0, 20, 40}, pressing keys 1..9 selects the corresponding class from the appropriate window of 9.

**AC-3: Click**
FT-P-46 — clicking a class entry selects that class; outbound annotation save (if any) carries the right classId.

**AC-4: Fallback**
FT-P-47 — when `/api/annotations/classes` returns 200 with `[]` or any 5xx, the fallback class list is rendered; tests assert the fallback length and a marker indicating fallback mode.

## System Under Test Boundary

- System under test: `<DetectionClasses>` + `<PhotoModeContext>` (read-only here).
- Allowed stubs: MSW for `/api/annotations/classes`.
- Disallowed: stubbing `<DetectionClasses>` or reading its React state.
- Expected observables per `results_report.md` rows 73-77 (Group 16).

## Constraints

- `seed_classes` MUST satisfy N≥9 (per test-data.md) so all hotkeys 1..9 are hot in P=0.
