Atlas adds a regression test to a Vue project by writing the failing spec first, proving it reproduces the bug, and only then fixing the code. The order is red before green. Atlas reproduces the bug with the bash tool, writes a Vitest with Vue Test Utils spec next to the offending single-file component, runs it through pnpm, watches it fail, applies the fix with edit, and re-runs the same command. Because the bash tool records the process exit code in its metadata alongside the output, the failing and passing states are unambiguous rather than a judgment call about log text.
How does Atlas add a regression test for a Vue bug fix?
Atlas adds a regression test to a Vue codebase in five moves: reproduce, write, fail, fix, re-run. The bug is reproduced once with the bash tool, the spec is written with the write tool against the real .vue component, and Vitest with Vue Test Utils supplies the verdict in 2026.
Atlas starts by reproducing the bug in the Vue app with a single bash invocation, capturing the exact failing command and its output. Atlas then uses the write tool to add a spec file, typically src/components/__tests__/PriceTag.spec.ts, that mounts the single-file component with Vue Test Utils and asserts on the wrong behavior you actually observed. The spec is run with pnpm through the bash tool. Only after the spec fails for the right reason does Atlas touch src/components/PriceTag.vue with the edit tool.
What Vue commands does Atlas actually run to prove the test fails?
Atlas runs Vitest with Vue Test Utils through pnpm and reads the exit code, not the prose. A single spec is targeted so the output stays small. In 2026 that is one bash call, and the bash tool records the process exit code in its metadata alongside the output.
The real command Atlas issues is a pnpm script that runs the spec by path, for example a pnpm test invocation scoped to src/components/__tests__/PriceTag.spec.ts. A nonzero exit code recorded by the bash tool is the proof that the regression test reproduces the bug. Atlas does not infer failure from a red word in the terminal. After the fix lands, Atlas re-runs the identical pnpm command, and a zero exit code is the proof of green. Running the full Vue suite afterwards checks for collateral damage across other single-file components.
Where should the Vue regression test file live?
A Vue regression test belongs beside the component it pins, usually in a __tests__ directory next to the .vue file, with a .spec.ts suffix that Vitest with Vue Test Utils already picks up. Atlas reads your existing Vue project layout in 2026 before choosing a path.
Atlas uses the read tool on your vite.config.ts, your package.json, and a couple of existing specs so the new file matches the conventions already in the Vue repo instead of inventing a new one. If your project keeps specs under tests/unit rather than a colocated __tests__ folder, Atlas follows that. The spec itself mounts the single-file component or exercises a Composition API composable directly, and prettier keeps the formatting consistent with the rest of the Vue codebase.
How does Atlas apply the Vue fix without breaking neighboring code?
Atlas applies the Vue fix with the edit tool at step 4 of the 5 step workflow, and its replacer cascade requires an exact-enough oldString and refuses ambiguous multi-match replacements. Atlas computes a unified diff for every file edit and surfaces it for approval before writing, so no line of your .vue file changes unreviewed.
Editing a Vue single-file component is risky precisely because the same expression can appear in the template block, the script setup block, and a sibling component. The edit tool will not guess: if the oldString matches in more than one place ambiguously, the replacement is refused rather than applied to the wrong block. You see the unified diff before it is written. Atlas also snapshots file changes as git patches, so if the fix to src/components/PriceTag.vue turns out to be wrong, the edit can be diffed and rolled back.
How do I review and approve what Atlas changes in a Vue project?
Every Atlas tool call is permission-gated against allow, ask, and deny rules before it runs, so a pnpm command or a write into src/components can be set to ask. In 2026, a Vue developer reviews the unified diff and the exit code, not a summary.
Review in a Vue project has two artifacts. The first is the unified diff Atlas surfaces before writing to any .vue file or spec. The second is the bash output with its recorded exit code, which tells you the regression test genuinely went from failing to passing. Permission rules let you allow reads across src, ask on writes, and deny anything you do not want an agent running. Running prettier after the fix keeps the diff limited to the behavior change instead of formatting churn.
Step by step
- 01Run atlas in your Vue project, the one with a package.json, and let Atlas read your .vue components, stores, and router.
- 02Reproduce the bug once with the bash tool and capture the exact failing command and output.
- 03Have Atlas write the regression test with the write tool, mounting the single-file component with Vue Test Utils and asserting on the observed wrong behavior.
- 04Run just that spec with pnpm through the bash tool and confirm Vitest with Vue Test Utils fails; the tool records the process exit code in its metadata alongside the output.
- 05Apply the fix with the edit tool, whose replacer cascade requires an exact-enough oldString and refuses ambiguous multi-match replacements across the template and script setup blocks.
- 06Review the unified diff Atlas surfaces for the .vue file before it is written.
- 07Re-run the same pnpm command and confirm Vitest with Vue Test Utils now passes.
- 08Run the wider Vue suite to check for collateral damage, then run prettier so the diff stays limited to the behavior change.
Frequently asked questions
- how to write a regression test in vue with an ai coding agent
- Ask Atlas to reproduce the bug with the bash tool first, then have it use the write tool to add a Vitest with Vue Test Utils spec that asserts on the wrong behavior. Run it with pnpm and confirm it fails before any fix is applied.
- does atlas run vitest with vue test utils itself
- Yes. Atlas runs Vitest with Vue Test Utils through the bash tool using your pnpm script. The bash tool records the process exit code in its metadata alongside the output, so Atlas knows the spec failed rather than guessing from the log text.
- how do i stop atlas from editing the wrong part of a .vue file
- The edit tool's replacer cascade requires an exact-enough oldString and refuses ambiguous multi-match replacements, so a string that appears in both the template block and the script setup block will not be silently swapped. Atlas also shows the unified diff before writing.
- can atlas add tests to an existing vue composition api codebase
- Yes. Run atlas in a Vue project with a package.json, let it read your .vue components, stores, and router, then ask it to add Vitest tests or migrate to the Composition API. Review the diff before it is written.
- how do i revert an atlas change to a vue component
- Atlas snapshots file changes as git patches, so any edit to a .vue file can be diffed and rolled back. Atlas also reads git branches, status, and diffs, and can stage and create commits on your behalf once the regression test passes.
- should i run the whole vue test suite after a bug fix
- Yes. After the targeted spec goes green, run the wider suite with pnpm to check for collateral damage in other single-file components, then run prettier so the final diff shows the behavior change and not formatting churn.
- can i require approval before atlas runs a pnpm command
- Yes. Every Atlas tool call is permission-gated against allow, ask, and deny rules before it runs, so you can set bash to ask, allow reads across src, and deny anything you do not want executed in your Vue project.
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