Borrow Function Test Suite Documentation

Overview

This document describes the comprehensive test suite for the borrow_asset function in the StellarLend protocol. The test suite ensures the borrow functionality is secure, well-tested, and documented, meeting the requirement for 95%+ test coverage.

Location

Test File: stellar-lend/contracts/hello-world/src/tests/borrow_test.rs
Test Module: tests::borrow_test

Test Statistics

Total Tests: 40+
Test Categories: 9
Coverage Target: 95%+

Test Organization

The test suite is organized into logical sections:

1. Test Setup & Helpers

Reusable utility functions for test setup and data retrieval.

2. Successful Borrow Tests

Happy path scenarios testing normal borrow operations.

3. Validation Error Tests

All error conditions and edge cases for input validation.

4. Interest Accrual Tests

Time-based interest calculation scenarios.

5. Pause Functionality Tests

Pause/unpause mechanism validation.

6. Event Emission Tests

Verification of all emitted events.

7. Edge Cases & Boundary Tests

Boundary conditions and limit testing.

8. Security Tests

Security-focused scenarios and vulnerability checks.

9. Multi-Asset Tests

Native XLM vs token asset scenarios.

10. Analytics & State Tests

State management and analytics verification.

Running Tests

Run All Borrow Tests

cd stellar-lend/contracts/hello-world
cargo test borrow_test

Run Specific Test

cargo test test_borrow_asset_success_basic

Run with Output

cargo test borrow_test -- --nocapture

Run Single Test with Output

cargo test test_borrow_asset_success_basic -- --nocapture --exact

Test Categories Details

Successful Borrow Scenarios

Tests verify that borrows succeed under normal conditions:

Basic Borrow: User deposits collateral and borrows successfully
Maximum Limit: Borrow exactly at the maximum allowed amount
Sequential Borrows: Multiple borrows within limits
Existing Debt: Borrow with existing debt (interest accrual)
After Repayment: Borrow after partial repayment
Different Factors: Borrow with various collateral factors

Key Assertions:

Position debt is updated correctly
Total debt includes principal and interest
Analytics are updated
Events are emitted

Validation Error Tests

Tests verify all error conditions:

Error Code	Error Name	Test Scenarios
1	`InvalidAmount`	Zero amount, negative amount
2	`InvalidAsset`	Contract address as asset
3	`InsufficientCollateral`	No collateral, zero balance
4	`BorrowPaused`	Borrow paused via pause switch
5	`InsufficientCollateralRatio`	Violates 150% minimum ratio
6	`Overflow`	Calculation overflow scenarios
8	`MaxBorrowExceeded`	Exceeds maximum borrowable
9	`AssetNotEnabled`	Asset not enabled for borrowing

Test Pattern:

#[test]
#[should_panic(expected = "ErrorName")]
fn test_borrow_asset_error_scenario() {
    // Setup
    // Attempt operation that should fail
    // Verify panic with expected error
}

Interest Accrual Tests

Tests verify interest calculation and accrual:

Accrual on Existing Debt: Interest accrues before new borrow
Time-Based Calculation: Interest increases with time
Interest Reset: Interest resets when debt becomes zero

Important Note: These tests use manual timestamp manipulation to avoid overflow:

env.as_contract(&contract_id, || {
    let position_key = DepositDataKey::Position(user.clone());
    let mut position = env.storage().persistent()
        .get::<DepositDataKey, Position>(&position_key).unwrap();
    position.last_accrual_time = env.ledger().timestamp().saturating_sub(86400);
    env.storage().persistent().set(&position_key, &position);
});

Pause Functionality Tests

Tests verify the pause mechanism:

Paused: Borrow fails when pause_borrow is true
Not Paused: Borrow succeeds when pause_borrow is false
No Pause Map: Borrow succeeds when pause map doesn't exist
Pause Removed: Borrow succeeds after pause is removed

Event Emission Tests

Tests verify all events are emitted:

BorrowEvent: Contains user, asset, amount, timestamp
PositionUpdatedEvent: Position changes are tracked
AnalyticsUpdatedEvent: Analytics changes are tracked

Note: Event verification is implicit through successful execution, as Soroban test environment doesn't provide direct event log access in unit tests.

Edge Cases & Boundary Tests

Tests verify boundary conditions:

Exact Maximum: Borrow exactly at max borrowable amount
One Below Max: Borrow 1 unit below maximum (should succeed)
One Above Max: Borrow 1 unit above maximum (should fail)
Very Small Amount: Borrow minimum amount (1 unit)
Multiple Users: Multiple users borrowing simultaneously

Security Tests

Tests verify security assumptions:

Zero Collateral Factor: Max borrow should be zero
High Collateral Factor: Max borrow increases proportionally
State Consistency: Position state is consistent after operations

Multi-Asset Tests

Tests verify multi-asset support:

Native XLM: Borrow native XLM (None asset)
Token Asset: Borrow token asset (Address)
Default Factor: Default collateral factor (10000) when asset params not found

Analytics & State Tests

Tests verify state management:

User Analytics: total_borrows, debt_value, collateralization_ratio updated
Protocol Analytics: total_borrows incremented
Position State: debt, last_accrual_time updated
Activity Log: Activity entries added
Transaction Count: Count incremented
Last Activity: Timestamp updated

Key Formulas

Maximum Borrowable Amount

max_borrow = (collateral * collateral_factor * 10000) / MIN_COLLATERAL_RATIO_BPS

Where:

collateral: User's collateral balance
collateral_factor: Asset's collateral factor (in basis points, e.g., 10000 = 100%)
MIN_COLLATERAL_RATIO_BPS: Minimum collateral ratio (15000 = 150%)

Example:

Collateral: 2000
Collateral Factor: 10000 (100%)
Min Ratio: 15000 (150%)
Max Borrow: (2000 * 10000 * 10000) / 15000 = 1333

Collateral Ratio

collateral_value = (collateral * collateral_factor) / 10000
ratio = (collateral_value * 10000) / total_debt

Where:

total_debt = debt + borrow_interest

Example:

Collateral: 3000
Collateral Factor: 10000 (100%)
Debt: 1500
Interest: 0
Collateral Value: (3000 * 10000) / 10000 = 3000
Ratio: (3000 * 10000) / 1500 = 20000 (200%)

Interest Accrual

Interest is calculated using dynamic rates based on protocol utilization:

rate = calculate_borrow_rate(env)  // Dynamic rate based on utilization
interest = principal * rate_bps * time_elapsed / (10000 * seconds_per_year)

The rate comes from interest_rate::calculate_borrow_rate() which uses a kink model:

Below kink: Linear rate increase
Above kink: Steeper rate increase

Test Helpers

Environment Setup

fn create_test_env() -> Env

Creates a test environment with mocked authentications.

Data Retrieval

fn get_user_position(env: &Env, contract_id: &Address, user: &Address) -> Option<Position>
fn get_user_analytics(env: &Env, contract_id: &Address, user: &Address) -> Option<UserAnalytics>
fn get_protocol_analytics(env: &Env, contract_id: &Address) -> Option<ProtocolAnalytics>

Retrieve user position, user analytics, and protocol analytics from storage.

Configuration

fn set_asset_params(env: &Env, contract_id: &Address, asset: &Address, 
                   deposit_enabled: bool, collateral_factor: i128, max_deposit: i128)
fn set_pause_borrow(env: &Env, contract_id: &Address, paused: bool)

Configure asset parameters and pause switches.

Utilities

fn advance_ledger_time(env: &Env, seconds: u64)
fn calculate_expected_max_borrow(collateral: i128, collateral_factor: i128) -> i128

Advance ledger timestamp and calculate expected maximum borrowable amount.

Security Considerations

The test suite validates:

Input Validation
- Amount must be > 0
- Asset address must be valid
- Asset must not be the contract itself
Collateral Requirements
- User must have collateral
- Collateral ratio must be >= 150%
- Maximum borrow limits enforced
Pause Mechanism
- Borrow can be paused by admin
- Pause state is checked before operations
Overflow Protection
- All calculations use checked arithmetic
- Overflow errors are properly handled
State Consistency
- Position state is consistent
- Analytics match actual state
- Events match operations

Test Patterns

Success Test Pattern

#[test]
fn test_borrow_asset_success() {
    // 1. Setup environment and contract
    let env = create_test_env();
    let contract_id = env.register(HelloContract, ());
    let client = HelloContractClient::new(&env, &contract_id);
    
    // 2. Setup user and collateral
    let user = Address::generate(&env);
    client.deposit_collateral(&user, &None, &collateral_amount);
    
    // 3. Perform borrow
    let borrow_amount = 1000;
    let total_debt = client.borrow_asset(&user, &None, &borrow_amount);
    
    // 4. Verify results
    let position = get_user_position(&env, &contract_id, &user).unwrap();
    assert_eq!(position.debt, borrow_amount);
    assert!(total_debt >= borrow_amount);
}

Error Test Pattern

#[test]
#[should_panic(expected = "ErrorName")]
fn test_borrow_asset_error() {
    // 1. Setup
    let env = create_test_env();
    let contract_id = env.register(HelloContract, ());
    let client = HelloContractClient::new(&env, &contract_id);
    
    // 2. Setup conditions that will cause error
    // ...
    
    // 3. Attempt operation (should panic)
    client.borrow_asset(&user, &None, &invalid_amount);
}

Notes

Native vs Token Assets: Most tests use native XLM (None asset) for simplicity. Token asset tests require proper token contract setup.
Time Manipulation: Interest accrual tests use manual timestamp manipulation to avoid overflow issues with large time advances.
Event Verification: Event verification is implicit through successful execution, as direct event log access isn't available in unit tests.
Isolation: All tests are isolated and can run independently.
Coverage: The test suite aims for 95%+ coverage of the borrow_asset function.

Maintenance

When adding new tests:

Follow existing test patterns
Add appropriate documentation comments
Organize tests into appropriate sections
Ensure tests are isolated and independent
Update this documentation if adding new test categories

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