Explain the difference between Stubs and Drivers in Integration Testing

Stubs:

• Dummy modules that simulate lower-level components
• Called by the module being tested (downward calls)
• Used in top-down integration testing
• Provide controlled responses to test upper-level logic

Drivers:

• Dummy modules that simulate higher-level components
• Call the module being tested (upward calls)
• Used in bottom-up integration testing
• Initiate test scenarios and validate responses

Example Implementation:

// Stub example for top-down testing
public class PaymentServiceStub {
    public PaymentResult processPayment(PaymentRequest request) {
        // Return controlled test response
        return new PaymentResult("SUCCESS", "TXN-123");
    }
}

// Driver example for bottom-up testing  
public class OrderServiceDriver {
    public void testInventoryService() {
        InventoryService service = new InventoryService();
        boolean result = service.checkAvailability("PRODUCT-123", 5);
        assert result == true;
    }
}