In reliability testing terminology, what is recovery or error testing and what does it try to measure about a software system?

Introduction / Context:
Recovery or error testing is part of reliability and robustness testing. Its aim is to confirm that a system can handle unexpected failures gracefully. Interviewers use this question to see whether candidates can think beyond happy path scenarios and consider what happens when components fail, networks drop or resources become unavailable.

Given Data / Assumptions:
- The system may experience crashes, network problems or hardware issues during operation.
- Users expect not to lose important data when such failures occur.
- The system should be able to restart, reconnect or roll back consistently after a problem.
- No mathematical calculation is required; the answer is conceptual.

Concept / Approach:
Recovery testing deliberately forces error conditions. For example, the tester may unplug network cables, stop database services or simulate power loss during a transaction. After the failure, the tester observes whether the system detects the issue, logs it appropriately and recovers to a safe state. Important aspects include data integrity, continuity of operations, clarity of error messages and whether manual intervention is required. The better the recovery behaviour, the more resilient the system is in real world conditions.

Step-by-Step Solution:
Step 1: Recall that recovery or error testing is about dealing with failures, not just normal operations. Step 2: Focus on options that describe system behaviour after crashes or interruptions. Step 3: Option a mentions crashes, hardware failures, network interruptions and returning to a stable state without data loss. Step 4: This matches standard definitions of recovery testing in reliability engineering. Step 5: Therefore, option a is the correct answer.

Verification / Alternative check:
To verify, think of a banking application where a transfer is in progress when network connectivity is lost. Recovery testing would check whether the transaction is completed, rolled back or flagged correctly and whether the account balances remain accurate. The central concern is data integrity and safe recovery, which is captured in option a and not in the other options.

Why Other Options Are Wrong:
Option b talks only about spelling in error messages, which is a minor usability issue, not recovery behaviour. Option c confuses recovery testing with load or capacity testing. Option d focuses solely on graphical layout, which does not address system stability or error handling at all.

Common Pitfalls:
A common pitfall is to test only graceful shutdown scenarios, while real failures are sudden and unplanned. Another mistake is not preparing clean test environments to simulate failures safely, which may lead to misleading results. It is also easy to forget to test the logging and monitoring aspects that help operators detect and respond to problems quickly.

Final Answer:
It evaluates how well a system can recover from crashes, hardware failures, network interruptions or other error conditions and return to a stable state without losing data or causing corruption.