| --- |
| license: cc-by-4.0 |
| pretty_name: "Receipts: do the tests in a fix catch the bug?" |
| language: |
| - en |
| tags: |
| - code |
| - testing |
| - software-engineering |
| - ai-agents |
| - coding-agents |
| - claude |
| - claude-code |
| - agent-skills |
| - pull-requests |
| - red-green |
| - tdd |
| size_categories: |
| - n<1K |
| task_categories: |
| - text-classification |
| configs: |
| - config_name: changes |
| data_files: data/changes.jsonl |
| default: true |
| - config_name: tests |
| data_files: data/tests.jsonl |
| --- |
| |
| # Receipts study: do the tests in a fix catch the bug? |
|
|
|  |
|
|
| 181 real code changes from 17 open-source repositories. For each one, every test the change added or edited was run twice: with the change, and with the changed source files reverted to the parent commit or the pull request's merge base. A test for a fix should fail without it. |
|
|
| Made with [Receipts](https://github.com/syntaxixr/receipts), which does this check for any pull request (CLI, GitHub Action, and a skill for Claude Code and other coding agents). |
|
|
| Try it on your own branch, nothing to install: `npx github:syntaxixr/receipts check` |
|
|
| ## Results |
|
|
| | | Changes | Judged | Proven | Mixed | Unproven | Weak only | |
| |---|---|---|---|---|---|---| |
| | Maintainer fix commits | 81 | 71 | 64 (90%) | 2 (3%) | 5 (7%) | 0 (0%) | |
| | Agent pull requests | 100 | 91 | 75 (82%) | 5 (5%) | 2 (2%) | 9 (10%) | |
|
|
| Percentages are of judged changes. The gap that shows up only in agent work is *weak only*: every test fails on the old code just because it imports a name the change adds, so no test ever runs against the old behavior. No maintainer commit had that shape. |
|
|
| ## Configurations |
|
|
| - **`changes`** (default): one row per change. `group` is `maintainer` (fix commits on the default branch) or `agent` (pull requests whose commits carry a coding agent's fingerprint: Claude Code, Codex, Cursor, Copilot). `outcome` is `proven`, `mixed`, `unproven`, `weak`, or `env` when the tests could not be judged in this environment. The verdict columns count the change's tests per verdict. |
| - **`tests`**: one row per judged test, with its verdict and the raw outcomes with and without the change (`with_change`, `without_change`; failures were re-run to spot flakes). |
|
|
| ## Verdicts |
|
|
| | Verdict | With the change | Without it | Meaning | |
| |---|---|---|---| |
| | PROVEN | passes | fails | The test catches what the change fixes | |
| | GUARD | passes | passes | Guards neighboring behavior next to a PROVEN test | |
| | THEATER | passes | passes | No test proves the change | |
| | WEAK | passes | fails on import | The code it calls did not exist yet | |
| | BROKEN | fails | | The change does not pass its own test | |
| | FLAKY | mixed | mixed | Different results on the same code | |
| | SKIPPED | skipped | | The test did not run | |
| | PRESERVED / CHANGED | | | For behavior-preserving changes: passes on both sides / fails on the old code | |
|
|
| ## Method and caveats |
|
|
| Maintainer sample: recent single-parent commits on the default branch whose message mentions a fix, a bug or an issue, and that change both code and tests (click, itsdangerous, markupsafe, sqlparse, humanize, marshmallow, more-itertools, tomlkit, dateutil, dayjs, ufo, defu). Agent sample: up to 20 pull requests per repository, newest first, open and closed alike (anthropics/claude-agent-sdk-python, openai/openai-agents-python, PrefectHQ/fastmcp, modelcontextprotocol/python-sdk, simonw/llm). |
|
|
| Each project was installed once at the tip of its default branch, so older changes can fail for environmental reasons; those are `env` and excluded from the percentages. The samples are small and not random: the numbers describe these projects, not the ecosystem. "Agent-authored" means an agent's fingerprint appears in the PR's commits; humans steer those agents. Full method: [docs/study.md](https://github.com/syntaxixr/receipts/blob/main/docs/study.md). Scripts to reproduce: [study/](https://github.com/syntaxixr/receipts/tree/main/study). |
|
|
| ## License |
|
|
| The data (verdicts, test ids, commit subjects and links) is released under CC BY 4.0. The code it describes belongs to its projects under their own licenses. |
|
|
