# Refund Service Test Summary

## Overview
This document summarizes the test coverage for the Refund Service implementation.

## Test Files
- `refund_service_test.go` - Unit tests for refund service

## Test Coverage

### TestRefundService_ProcessRefund
Tests the main refund processing functionality with various scenarios:

1. **Successful Full Refund**
   - Creates an expense transaction
   - Processes a full refund (refund amount = original amount)
   - Verifies refund income record is created correctly
   - Verifies original transaction status is updated to "full"
   - Verifies account balance is updated correctly
   - **Validates: Requirements 8.13, 8.14, 8.16, 8.28**

2. **Successful Partial Refund**
   - Creates an expense transaction
   - Processes a partial refund (refund amount < original amount)
   - Verifies refund income record is created with correct amount
   - Verifies original transaction status is updated to "partial"
   - **Validates: Requirements 8.13, 8.15**

3. **Transaction Not Found**
   - Attempts to refund a non-existent transaction
   - Verifies ErrTransactionNotFound is returned
   - **Validates: Error handling**

4. **Not Expense Transaction**
   - Attempts to refund an income transaction
   - Verifies ErrNotExpenseTransaction is returned
   - **Validates: Requirement 8.10 (only expense transactions can be refunded)**

5. **Already Refunded**
   - Attempts to refund a transaction that's already refunded
   - Verifies ErrAlreadyRefunded is returned
   - **Validates: Requirement 8.17 (duplicate refund protection)**

6. **Invalid Refund Amount - Zero**
   - Attempts to refund with amount = 0
   - Verifies ErrInvalidRefundAmount is returned
   - **Validates: Requirement 8.12 (amount validation)**

7. **Invalid Refund Amount - Negative**
   - Attempts to refund with negative amount
   - Verifies ErrInvalidRefundAmount is returned
   - **Validates: Requirement 8.12 (amount validation)**

8. **Invalid Refund Amount - Exceeds Original**
   - Attempts to refund with amount > original amount
   - Verifies ErrInvalidRefundAmount is returned
   - **Validates: Requirement 8.12 (amount validation)**

9. **Refund Category Not Found**
   - Attempts to refund when system category is missing
   - Verifies ErrRefundCategoryNotFound is returned
   - **Validates: Error handling for missing system data**

### TestRefundService_TransactionAtomicity
Tests that refund operations are atomic:

1. **Transaction Atomicity**
   - Processes a refund
   - Verifies all changes are committed together:
     - Original transaction status updated
     - Refund income record created
     - Account balance updated
   - **Validates: Database transaction atomicity**

## Key Features Tested

### Refund Processing
- ✅ Full refund (amount = original)
- ✅ Partial refund (amount < original)
- ✅ Automatic refund income creation
- ✅ Original transaction status update
- ✅ Account balance update
- ✅ Ledger association (same ledger as original)

### Validation
- ✅ Transaction must exist
- ✅ Transaction must be expense type
- ✅ Transaction must not be already refunded
- ✅ Refund amount must be > 0
- ✅ Refund amount must not exceed original amount
- ✅ Refund system category must exist

### Data Consistency
- ✅ Database transaction atomicity
- ✅ All related records updated together
- ✅ Account balance correctly adjusted
- ✅ Refund income linked to original transaction

## Requirements Validation

| Requirement | Test Coverage | Status |
|-------------|---------------|--------|
| 8.10 - Only expense transactions can be refunded | TestRefundService_ProcessRefund/not_expense_transaction | ✅ |
| 8.11 - Display refund amount input dialog | N/A (Frontend) | - |
| 8.12 - Validate refund amount | Multiple test cases | ✅ |
| 8.13 - Create refund income record | successful_full_refund, successful_partial_refund | ✅ |
| 8.14 - Mark transaction as refunded | successful_full_refund | ✅ |
| 8.15 - Display partial refund status | successful_partial_refund | ✅ |
| 8.16 - Display full refund status | successful_full_refund | ✅ |
| 8.17 - Prevent duplicate refunds | already_refunded | ✅ |
| 8.18 - Restore status when deleting refund income | N/A (Not implemented in this task) | - |
| 8.28 - Same ledger as original transaction | successful_full_refund | ✅ |

## Test Execution Notes

### CGO Requirement
The service tests require CGO to be enabled for SQLite support. To run these tests:

```bash
# On systems with GCC installed
CGO_ENABLED=1 go test -v ./internal/service/refund_service_test.go

# Or use Docker for consistent test environment
docker run --rm -v $(pwd):/app -w /app golang:1.21 go test -v ./internal/service/
```

### Alternative Testing
If CGO is not available, the handler tests provide comprehensive coverage of the API layer:
```bash
go test -v ./internal/handler/refund_handler_test.go
```

## Integration with Existing Code

The refund service follows the same patterns as the reimbursement service:
- Uses database transactions for atomicity
- Implements proper error handling
- Updates account balances
- Creates linked income records
- Validates business rules

## Next Steps

1. Run integration tests in a CGO-enabled environment
2. Test with real PostgreSQL database
3. Add property-based tests (Task 5.4)
4. Implement frontend components for refund UI