Turning Bugs into Tests: A Practical Debugging Quiz Quiz

Explore effective debugging strategies by learning to convert bugs into automated tests. This quiz focuses on real-world software errors, test-driven bug resolution, and robust code quality techniques for reducing regressions.

1. Recognizing Bug Reproduction Patterns

   When you encounter a bug that only occurs after a sequence of user actions, what is the best first step to create a useful test case for this bug?

   1. Delete code segments until the bug disappears
   2. Guess which function is faulty and test it in isolation
   3. Immediately fix the bug in the code without writing a test
   4. Document the exact steps needed to reproduce the bug and use them to write the test

   Explanation: Documenting the steps ensures your test accurately mimics the bug scenario, providing reliable detection and preventing future regressions. Fixing the bug without a test risks introducing new errors or missing the core issue. Guessing the fault or deleting code is haphazard and unlikely to yield a reliable, repeatable test. Effective debugging requires careful reproduction as the basis for meaningful tests.

2. Understanding Regression Test Purpose

   Why is adding a test when fixing a discovered bug considered a best practice in software development?

   1. It guarantees the application is now completely bug-free
   2. It slows down software development unnecessarily
   3. It prevents the same bug from reappearing after future changes
   4. It serves only as a temporary fix

   Explanation: Writing a test for the specific bug ensures future updates do not accidentally reintroduce the same issue. It does not make the entire application bug-free, so that option is incorrect. Contrary to popular belief, adding targeted tests improves quality, not slows development. The added test remains useful over time and is not just a temporary solution.

3. Identifying Causes of Intermittent Failures

   A developer finds a bug that only triggers under certain timing conditions, causing non-deterministic test failures. Which test design approach is most effective in capturing this bug?

   1. Run the test hundreds of times hoping to catch the bug
   2. Remove any timing-dependent code from the application
   3. Ignore the bug since it is hard to reproduce
   4. Introduce controlled delays or mocks to reliably reproduce the timing conditions in the test

   Explanation: Using controlled delays or mocks helps create a repeatable test environment, making the issue detectable every time. Simply running the test many times is inefficient and unreliable. Ignoring the bug leaves it unresolved, while removing timing-related code can break required functionality. Structured test design is key for intermittent bugs.

4. Converting Production Bugs to Unit Tests

   If a bug is reported in production where a function returns null instead of a calculated value, which test should be created to ensure this bug is caught in the future?

   1. A performance test checking the response time of the function
   2. A unit test that accepts any output for the provided inputs
   3. A unit test that provides the same inputs as the real case and asserts the calculated value is returned
   4. A UI test clicking a random button in the application

   Explanation: A specific unit test with the problematic inputs ensures the calculation occurs and the bug does not recur. Accepting any output would miss the error, while a performance test won't necessarily check for functional correctness. A random UI test would not target the underlying logic producing the incorrect output.

5. Interpreting Test Failures After Bug Fix

   After fixing a bug and adding the corresponding test, which result most clearly indicates that your code change was successful?

   1. No tests run at all
   2. The new test fails, but unrelated tests pass
   3. The new test passes but previously passing tests now fail
   4. All tests, including the new one, pass consistently

   Explanation: Passing all tests, including the added test, shows that the bug is fixed and that existing functionality remains intact. If previous tests fail, you may have introduced other defects. A new test failing means the bug remains unresolved, and not running tests means the state of code correctness is unknown. Consistency across all tests is essential after a bug fix.