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When Cursor-generated code fails a test or breaks a working feature, pause further edits and use a repeatable repair loop: inspect the full diff, reproduce and classify the failure, define the intended behavior, make one narrow fix, add or update a regression test, and rerun the project’s checks. A green test run is useful evidence—not proof—so review the assertions and final patch before accepting it.
1. Preserve a reviewable baseline and inspect the change
Before asking Cursor to edit again, make sure you can compare the current files with the state before the generated change. Use your normal branch, commit, or patch workflow; no particular version-control command is required. Cursor’s diff and review interface lets you inspect additions and deletions and accept or reject changes at file or line level. Review beyond the line that appears to have failed: collateral edits elsewhere may be responsible for a regression.
If the change is clearly moving in the wrong direction, stop and redirect rather than layering more speculative edits on top. For a larger course correction, restore the reviewable baseline using your usual workflow, then give Cursor a clearer diagnosis and constraints.
2. Identify exactly what failed
Run the failing check again and record the command, complete error output, and smallest steps that reproduce the problem. Cursor’s Quickstart recommends reviewing generated changes and running checks already used by the project, such as tests, type checking, linting, or a local build.
#1 Best Overall
- Test failure: Note the failing test, assertion, and input.
- Type or lint error: Capture the diagnostic and the file or rule it identifies.
- Build failure: Record the build command and the first relevant error, while checking whether later messages are consequences of it.
- Runtime regression: Write down the steps, inputs, and observed behavior that differ from what worked before.
A failure appearing after a generated patch does not by itself establish that the patch caused it. Check whether it is in the changed code, a generated test, test setup, dependencies, or a pre-existing issue. Compare with the prior baseline when practical.
3. State the expected behavior and trace the affected code
Describe the desired result in observable terms: what input or action should produce what output or side effect? Compare that expectation with the failure, then inspect the edited code, its callers, and neighboring tests. Cursor’s bug-fixing guidance emphasizes reproducing issues, narrowing their cause, and verifying a fix; its code-review guidance also stresses considering surrounding context.
You can ask Cursor to trace the relevant call path and suggest plausible causes, but verify those connections in the code yourself. If the cause is not clear, ask for a short list of hypotheses and the evidence that would distinguish them before authorizing another edit.
4. Choose the investigation path that fits the evidence
| Situation | Start with | Next move |
|---|---|---|
| Repeatable test, type-check, lint, or build failure | The exact failing command and output | Use the focused failure to narrow the changed behavior, then run relevant broader checks. |
| Runtime regression with no clear failing check | Minimal reproduction steps and observed behavior | Test plausible causes with narrow instrumentation, then add a regression test once the behavior is understood. |
Neither path is universally better: the best starting point depends on whether a project check already captures the failure or you first need runtime evidence.
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5. Make one targeted repair
Give Cursor the failing command and output, reproduction steps, expected behavior, and constraints. Ask it to explain the likely root cause before editing, make the smallest repair, and identify any assumptions. Avoid asking for a broad rewrite when a narrow change can address the observed defect.
For a reproducible but opaque runtime bug, Cursor’s Debug Mode guidance describes forming hypotheses, adding focused logging, reproducing the issue while collecting runtime data, analyzing the observations, and then making a targeted fix. Keep instrumentation limited to what helps distinguish the likely causes, and remove temporary logging if it does not belong in the finished change.
6. Add a regression test without weakening the contract
When practical, add a test that captures the bug: it should fail against the broken behavior and pass after the repair. Preserve tests for neighboring behavior that used to work. Before a refactor, tests can also record existing behavior so you can detect accidental changes as you proceed. Cursor’s testing guide describes this behavior-locking and run-and-fix workflow, while cautioning that generated tests need review for meaningful assertions and correct setup.
A useful prompt is: “Reproduce the failing behavior, explain the likely cause before editing, make the smallest fix, add a regression test for the observed bug, and run the relevant existing checks. Do not remove or weaken an assertion unless you explain why its expected behavior is incorrect.” Treat this as a request for a proposed change, not a substitute for reviewing the result. If a test expectation changes, check that the intended product behavior—not merely the test—is wrong.
Best Value
7. Rerun checks and review the final patch
- Run the focused test or command that exposed the problem.
- Run relevant broader tests, then the project’s established type, lint, and build checks that apply to the change.
- Review the complete final diff, including files outside the apparent fix, and reject unrelated or unexplained edits.
- Read the regression test’s setup and assertions. Confirm it checks the desired behavior and meaningful edge cases, rather than merely matching the implementation Cursor produced.
Cursor’s review and testing guidance warns that generated code can look correct while still being subtly wrong, and that passing tests do not guarantee correctness when assertions or edge cases are inadequate. For a failure that occurs in CI, Cursor’s testing material also describes a CLI workflow for analyzing and fixing CI failures. That can help investigate, but it does not replace inspecting the proposed patch and rerunning the relevant checks.
Quick Recap
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