chore: update documentation

docs/PROJECT_OVERVIEW.md

@@ -122,6 +122,8 @@ Critical for correct pricing and auto-reassignment:
 - **Auto-reassignment**: Maintains insurance type when price tier changes
 - **Age constraints**: Absolute age (at travel date) vs birth year
 - **Hydration**: `TravelDataService::hydrateInsurancePackageRelationships()` rebuilds package relationships after cache deserialization
+- **ID Type**: Insurance IDs are strings (not integers) - ensure all test fixtures use string IDs
+- **Mutability**: Insurances are always readonly in edit mode (API limitation) - see `InsuranceMutabilityCondition`
 
 ### Transportation Services
 - **Unified pickup field**: Single field for both directions (BPN API limitation)
@@ -190,6 +192,13 @@ Critical for correct pricing and auto-reassignment:
 - Ensure dependencies declared correctly
 - Check sync pattern: only sync fields in original submission
 
+### Writing Tests
+- **Insurance IDs**: Always use strings, not integers (e.g., `'100'` not `100`)
+- **Room properties**: Use `$label` property, not `$name`
+- **Participant names**: Index 0 expects "Anmelder:in", others expect "Teilnehmer:in N" (1-based)
+- **Mock dependencies**: Ensure all constructor dependencies have mocks (especially new ones like `InsuranceLoader`, `InsuranceTypeFilterService`)
+- **Insurance mutability**: In edit mode, insurances are always readonly (API limitation)
+
 ## File Locations
 
 ### Key Design Patterns
@@ -295,12 +304,21 @@ Edit mode session requires proper cleanup to prevent dirty state persistence:
 ## Testing
 
 ```bash
-./vendor/bin/phpunit                              # All tests
+./vendor/bin/phpunit                              # All tests (182 tests, 465 assertions)
 ./vendor/bin/phpunit tests/Service/               # Service layer
 ./vendor/bin/phpunit tests/BusProNet/             # API integration
-./vendor/bin/php-cs-fixer fix                     # Code style (Symfony ruleset)
+./vendor/bin/phpunit tests/Form/                  # Form processing and field handlers
+/opt/homebrew/bin/php-cs-fixer fix --rules=@Symfony  # Code style (Symfony ruleset)
 ```
 
+**Test Coverage Areas:**
+- BusProNet data loaders and processors
+- XML parsers (travels, hotels, bookings, insurances)
+- Form DTOs and field handlers
+- Service layer (pricing, insurance matching, room assignment)
+- Conditional field system
+- Utility classes
+
 ## Development Environment
 
 ```bash
@@ -314,16 +332,19 @@ ddev exec "php -r 'opcache_reset()';"             # Clear opcache after code cha
 ## Important Notes
 
 - **Room prices are per person**
+- **Room model uses `$label` property** (not `$name`) - ensure test fixtures use correct property
 - **Zero prices display without suffix** (e.g., "Vollpension" not "Vollpension (€0,00)")
 - **All services sorted by price** (cheapest first) via `SortByPriceTrait`
 - **Field sync pattern critical**: Only sync fields in original submission to avoid "extra fields" errors
 - **Insurance handler requires mode awareness**: Skips processing in edit mode (API doesn't return insurance data)
+- **Insurance IDs are strings**: All insurance IDs must be strings, not integers (type safety)
 - **Clear opcache after code changes** affecting hydration or serialization
 - **HTMX targeting consistency**: All swaps target `#main-content` with `innerHTML`, sidebar via OOB swap
 - **Validation pattern**: Both create and edit flows use validation-only forms that wrap card UI for standard Symfony form handling
 - **Card error indicators**: `ParticipantValidationTrait::extractParticipantErrorIndices()` parses form errors to highlight invalid participant cards
 - **Edit mode service availability**: Services with `available <= 0` remain visible and editable for participants who already have them (prevents fingerprint false positives)
 - **Session cleanup on exit**: All exit paths from edit mode (save, discard, cancel) properly clear session to reset dirty state
+- **Participant naming convention**: Index 0 is "Anmelder:in", others are "Teilnehmer:in N" (1-based, not 0-based)
 
 ## References