Five Practical Ways to Improve and Maintain Code Written by Others

1. Ensure There Are Tests

When working with code written by another developer, you must verify that the existing functionality works as expected and that your changes will not break it; the only reliable way to gain confidence is through testing.

(1) Insufficient testing coverage.

(2) Adequate testing coverage.

If tests are lacking, you should create new ones to understand the code’s intent; if sufficient tests already exist, use them to confirm that your modifications do not introduce regressions.

Write New Tests

When you cannot rely on existing tests, write your own to capture the expected input‑output behavior, which also helps you learn the code’s purpose and edge cases.

Leverage Existing Tests

When adequate tests are present, study them to infer the original author’s understanding of the code; however, remain cautious of outdated tests that may mislead you.

2. Talk to the Original Author

Effective communication is essential; ask targeted questions such as which system component the code belongs to, design diagrams, potential pitfalls, component purpose, and any omitted intentions.

Which part of the system blueprint does this code correspond to?

Do you have related design documents or diagrams?

Are there any known pitfalls?

What is the purpose of this component or class?

Was there anything you intended to implement but didn’t, and why?

Approach the author with humility, assuming there is a rational reason behind decisions, and avoid over‑reliance on a single person to prevent tight coupling.

3. Eliminate All Warnings

Inspired by the "broken‑window" theory, leaving warnings or unused code encourages further neglect; proactively remove warnings, dead code, and annotate unavoidable ones to keep the codebase clean and maintainable.

It forces careful consideration of any new code.

It reduces the chance of future bugs caused by ignored warnings.

4. Refactor the Code

Refactoring means changing the internal structure without altering external behavior, making the code easier to understand and modify while ensuring all tests still pass.

5. Make the Code Better Than You Found It

Whenever you modify someone else’s code, aim to leave it in a better state—pay technical debt, improve readability, and ensure future developers can work with it confidently.

By applying these five methods, you can responsibly take ownership of legacy code, reduce risk, and continuously improve software quality.