Which testing approach involves running the new system in parallel with the existing system and comparing outputs?

Which testing approach involves running the new system in parallel with the existing system and comparing outputs?

• A. A/B Testing
• B. Parallel Testing
• C. Smoke Testing
• D. Regression Testing

Answer: (B)

Running the new system in parallel with the existing one and comparing outputs tests whether the new implementation reproduces the same results as the old one when given the same inputs. This approach, often used during migration or replacement, lets you validate functional behavior and data integrity before fully switching over. You feed identical data into both systems, compare the results line by line, and look for any discrepancies that could indicate differences in logic, rounding, or data handling. It helps catch issues that might not be evident from isolated testing and reduces risk of unexpected behavior after deployment. In contrast, A/B testing compares user-facing variants to measure impact on metrics, smoke testing is a quick check of critical paths, and regression testing focuses on re-running existing tests after changes to ensure nothing broke—none of these involve a controlled parallel run with exact output comparison across two systems.

Running the new system in parallel with the existing one and comparing outputs tests whether the new implementation reproduces the same results as the old one when given the same inputs. This approach, often used during migration or replacement, lets you validate functional behavior and data integrity before fully switching over. You feed identical data into both systems, compare the results line by line, and look for any discrepancies that could indicate differences in logic, rounding, or data handling. It helps catch issues that might not be evident from isolated testing and reduces risk of unexpected behavior after deployment. In contrast, A/B testing compares user-facing variants to measure impact on metrics, smoke testing is a quick check of critical paths, and regression testing focuses on re-running existing tests after changes to ensure nothing broke—none of these involve a controlled parallel run with exact output comparison across two systems.