How to Catch Hidden Assumption Errors in Your Code—And Can a Language Model Help?

Every developer has encountered a bug that “shouldn’t have happened.” Often, these bugs stem from hidden assumptions in the code.

Take the example of a system handling substitute employees. It assumes that every substitute is assigned to replace someone. But in reality, substitutes may exist because no one currently holds the position. This faulty assumption leads to a null pointer exception, and a database constraint failure makes things worse.

These issues could have been caught earlier. But how? Could a language model (LM) help uncover such flawed assumptions before they break production?

Understanding Assumption-Based Bugs

An assumption-based bug happens when code is built on an unchecked belief about how the system works.

In the substitute employee example:

  • The system assumes every substitute has a direct assignment.
  • In some cases, no one holds the position, making the assumption false.
  • This leads to a null pointer exception and a database constraint failure.

Such bugs are common because assumptions often go unchallenged during development.

Can a Language Model Help Detect These Issues?

LMs could assist by:

  1. Extracting assumptions from code and documentation.
  2. Identifying weak spots, comparing them to past failures.
  3. Suggesting fixes, pointing out missing cases or alternative logic.

While today’s LMs aren’t perfect at reasoning, they can help detect patterns and highlight potential problem areas.

Practical Ways to Reduce Assumption-Based Bugs

Even without an LM, there are ways to catch these issues early:

  • Document Assumptions – Clearly state system assumptions and challenge them.
  • Use Static Analysis Tools – Linters and type checkers can catch logic inconsistencies.
  • Implement Defensive Programming – Always check for null values and validate inputs.
  • Explore AI-Assisted Code Review – Emerging tools can help flag logical inconsistencies.

Conclusion

Many software bugs come from flawed assumptions rather than syntax errors. While LMs may assist in uncovering them, developers can take proactive steps today: document assumptions, use static analysis tools, and test for edge cases.

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