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After Claude Code changes code, run the project’s existing focused property test—not a guessed universal command—then inspect any generated counterexample and rerun after a fix. The exact test command depends on the repository’s language, test runner, and configured scripts.
1. Find the project’s test setup
Start in the project directory. Review the edited files, nearby tests, repository instructions, and package or build scripts. Identify the language, test runner, and property-testing library already in use. Claude Code works in the project context and can be asked to run tests for a module and investigate failures, but it does not supply one property-test command that applies to every repository. See Anthropic’s Claude Code documentation.
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Use the command and test-target conventions the project already defines. If the repository has a focused test for the edited behavior, run that first. Do not copy a command from another language or framework and assume it fits.
2. Identify the property the edit should preserve
Before running a test, state what general rule the changed code must satisfy. Base it on the function’s contract, types, documentation, call sites, and existing tests. A property-based test checks a general rule across generated inputs rather than only a few manually chosen examples. Anthropic’s workflow begins by understanding the target and proposing properties; the Hypothesis guide likewise emphasizes understanding the code before deciding what to test.
For example, if an edited function normalizes input, the invariant might be that normalizing an already normalized value leaves it unchanged. Treat that only as an illustration: the right property must come from the actual function contract, not from a generic recipe.
3. Run the focused property test
Use the repository’s configured test command and, where supported, target the relevant test or module. The framework generates valid inputs to look for a counterexample to the stated property. Anthropic describes this as searching for a counterexample by generating valid test inputs using techniques similar to fuzzing.
Anthropic’s article demonstrates Hypothesis in Python, but that is an example—not a requirement for Claude Code or a universal command. The title does not specify a project language, test file, or runner, so there is no responsible single command to give here.
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When a property test fails, inspect both the assertion and the generated input. Ask whether the implementation violates the intended invariant, or whether the property, input generator, or test setup is wrong. A failing example is evidence to investigate, not automatic proof that the code is defective. Anthropic’s workflow explicitly includes reflecting on whether a failure exposed a bug or the test needs adjustment.
5. Rerun after a fix and report what happened
After a code or test correction, run the focused property test again. Then run the relevant broader suite if the repository’s conventions provide one. Report the exact command that actually ran and its observed result; do not say a test passed unless you saw it pass. Claude Code’s documentation covers using tests to check changes and rerunning them to confirm a fix.
A passing run means the generated inputs checked by that test did not reveal a counterexample to that property. It is not proof of exhaustive correctness.
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A prompt to use with Claude Code
You can ask Claude Code to investigate and run the repository’s existing test without assuming a particular stack:
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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallInspect the edit and the project’s existing test setup. Identify the property this change should preserve, run the existing focused property test using the project’s command, and report the exact command and result. If it fails, show the counterexample and explain whether it indicates a code defect or a test issue before changing anything.
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This is suggested prompt wording, not a vendor-prescribed command. Claude Code also supports noninteractive claude -p operation for scripts and pipelines; that mode does not determine which property-test command the repository uses. See Anthropic’s CLI documentation.
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