Parallel Testing in System Implementation
Explore parallel testing approaches for system implementation and conversion. Learn audit considerations for parallel operations for the CISA exam.
What Is Parallel Testing?
Parallel testing (also called parallel running or parallel operation) involves operating both the old and new systems simultaneously for a period of time to verify that the new system produces the same results as the existing one. For CISA candidates, understanding parallel testing is important because it is one of the most reliable methods for validating a new system before fully transitioning from the legacy environment.
System Conversion Approaches
Parallel testing is one of several conversion approaches that organizations use when implementing new systems:
- Parallel operation: Both systems run simultaneously, processing the same transactions. Results are compared to verify accuracy. This is the safest approach but the most expensive and resource-intensive.
- Direct cutover (abrupt changeover): The old system is shut down and the new system goes live immediately. This is the riskiest approach because there is no fallback if the new system fails.
- Phased conversion: The new system is implemented in stages, with each stage replacing a portion of the old system. This distributes risk across multiple transitions.
- Pilot conversion: The new system is deployed to a limited group of users or a single location before full rollout. This tests the system in a real environment with limited exposure.
Planning Parallel Operations
Successful parallel testing requires thorough planning:
- Duration: Determine how long parallel operations will run. The duration should be sufficient to cover at least one complete business cycle, including month-end or period-end processing.
- Scope: Define which transactions, processes, and reports will be run in parallel. All critical business processes should be included.
- Resources: Parallel operation requires additional staff effort because employees must process transactions in both systems. Plan for adequate staffing during the parallel period.
- Comparison procedures: Define how results from both systems will be compared, what tolerance levels are acceptable, and how discrepancies will be investigated.
- Success criteria: Establish clear criteria for determining when the new system has been sufficiently validated to proceed with full transition.
Comparing Results
During parallel operation, organizations compare outputs from both systems including transaction processing results, report outputs, account balances and totals, and processing times and system performance. Discrepancies must be investigated to determine whether they result from errors in the new system, improvements that produce different but correct results, or differences in processing logic that need resolution.
Challenges of Parallel Testing
Parallel operation presents several challenges including the significant additional workload on staff, the risk of confusion between systems, the cost of maintaining two operational environments, and the difficulty of maintaining data synchronization between systems. Despite these challenges, parallel testing remains the preferred approach for mission-critical systems where the cost of failure is high.
Auditing Parallel Testing
IS auditors should evaluate parallel testing by reviewing the parallel testing plan for adequacy, verifying that comparison procedures are thorough, assessing whether discrepancies are properly investigated and resolved, confirming that success criteria are defined and met before the legacy system is retired, and evaluating whether the parallel period covered sufficient business cycles.
CISA Exam Tips
For the CISA exam, understand the different conversion approaches and their relative risks and benefits. Know that parallel operation is the safest approach and is recommended for critical systems. Questions may present implementation scenarios and ask which conversion approach is most appropriate given the risk profile.