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To run a property test after Claude Code edits your code, use the property-testing command already configured for the project, aimed at the test covering the changed behavior. There is no universal Claude Code property-test command: the right file, runner, and command depend on the repository. First identify the project’s test setup and the invariant the edit should preserve; then run the focused test, investigate any generated counterexample, and rerun after a fix.
Find the project’s existing test command
Start in the project directory. Inspect the changed files, nearby tests, repository instructions, and the project’s package or build scripts. Identify the language, test runner, and property-testing library already in use. Use the project’s established command rather than guessing from another language or framework.
Claude Code works in the project context and can be asked to run tests for a module and investigate failures. Its noninteractive claude -p mode can be used in scripts and pipelines, but it does not determine the test command: that still comes from the project’s configuration. See Anthropic’s Claude Code CLI reference.
Decide what property the edit should preserve
A property-based test checks a general rule over generated inputs, rather than checking only a handful of manually chosen examples. The property needs to express behavior the code is supposed to guarantee—not merely a condition that happens to be true for a few inputs.
Ground the invariant in the changed function’s contract, types, documentation, call sites, and existing tests. Anthropic’s workflow recommends understanding the target and proposing properties before writing tests; Hypothesis also emphasizes gathering context before choosing a property. See Anthropic’s property-based testing article and Hypothesis documentation.
Run the focused property test
Use the repository’s existing test command and, where the runner supports it, target the test or module relevant to the edit. The framework generates valid inputs to search for a counterexample to the property. Anthropic describes this as searching for a counterexample by generating inputs in a way similar to fuzzing.
Do not assume a Python or Hypothesis command applies to another project. If the repository has no property test for the changed behavior, identify the existing framework and test conventions before adding one; the right test file, generator, and command cannot be determined without the project’s language and setup.
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Interpret failures before changing code
When a run fails, inspect the generated input and the assertion that failed. Then decide whether the implementation violates the intended invariant or whether the property, input generator, or test setup is incorrect. A counterexample is evidence to investigate, not automatic proof that the implementation is wrong. Anthropic’s workflow calls for evaluating whether a failure exposes a bug or whether the test itself needs adjustment.
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Rerun after a fix and report what happened
After changing the implementation or test, rerun the focused property test. Then run the relevant broader suite if the repository’s conventions call for it. Report the exact command that ran and its observed result; do not describe a test as passing unless it actually passed. A passing run means the generated inputs checked under that property did not expose a counterexample—it is not proof of exhaustive correctness.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.A prompt to use with Claude Code
You can ask Claude Code to inspect the edit and run the project’s configured test without implying that a particular command is universal:
Inspect 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.
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