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Vitest Contributing Guide

Hi! We are really excited that you are interested in contributing to Vitest. Before submitting your contribution, please make sure to take a moment and read through the following guide:

Repo Setup

The Vitest repo is a monorepo using pnpm workspaces. The package manager used to install and link dependencies must be pnpm.

We recommend installing ni to help switching between repos using different package managers. ni also provides the handy nr command which running npm scripts easier:

  • ni is equivalent to pnpm install
  • nr test is equivalent to pnpm run test

To develop and test vitest package:

  1. Run pnpm install in vitest's root folder

  2. Run pnpm run dev to build sources in watch mode

  3. Run

    • pnpm run test to run core tests
    • pnpm run test:all to run all the suite

💡 If you use VS Code, you can hit ⇧ ⌘ B or Ctrl + Shift + B to launch all the necessary dev tasks.

Debugging

VS Code

If you want to use break point and explore code execution you can use the "Run and debug" feature from vscode.

  1. Add a debugger statement where you want to stop the code execution.

  2. Click on the "Run and Debug" icon in the activity bar of the editor.

  3. Click on the "Javascript Debug Terminal" button.

  4. It will open a terminal, then type the test command: pnpm run test

  5. The execution will stop and you'll use the Debug toolbar to continue, step over, restart the process...

Testing Vitest against external packages

You may wish to test your locally-modified copy of Vitest against another package that is using it. For pnpm, after building Vitest, you can use pnpm.overrides. Please note that pnpm.overrides must be specified in the root package.json and you must first list the package as a dependency in the root package.json:

{
  "dependencies": {
    "vitest": "*"
  },
  "pnpm": {
    "overrides": {
      "vitest": "link:../path/to/vitest/packages/vitest"
    }
  }
}

And re-run pnpm install to link the package.

Add a .npmrc file with following line next to the package.json:

VITE_NODE_DEPS_MODULE_DIRECTORIES=/node_modules/,/packages/

Pull Request Guidelines

  • Checkout a topic branch from a base branch, e.g. main, and merge back against that branch.

  • If adding a new feature:

    • Add accompanying test case.
    • Provide a convincing reason to add this feature. Ideally, you should open a suggestion issue first and have it approved before working on it.

  • If fixing bug:

    • If you are resolving a special issue, add (fix #xxxx[,#xxxx]) (#xxxx is the issue id) in your PR title for a better release log, e.g. fix: update entities encoding/decoding (fix #3899).
    • Provide a detailed description of the bug in the PR. Live demo preferred.
    • Add appropriate test coverage if applicable.

  • It's OK to have multiple small commits as you work on the PR - GitHub can automatically squash them before merging.

  • Make sure tests pass!

  • Commit messages must follow the commit message convention so that changelogs can be automatically generated.

  • Use pnpm run lint:fix to format files according to the project guidelines.

Maintenance Guidelines

The following section is mostly for maintainers who have commit access, but it's helpful to go through if you intend to make non-trivial contributions to the codebase.

Issue Triaging Workflow

flowchart TD
    start{Followed issue\ntemplate?}
    start --NO--> close1[Close and ask to\nfollow template]
    start --YES--> dupe{Is duplicate?}
    dupe --YES--> close2[Close and point\nto duplicate]
    dupe --NO--> repro{Has proper\nreproduction?}
    repro --NO--> close3[Label: 'needs reproduction'\nbot will auto close if no update\nhas been made in 3 days]
    repro --YES--> real{Is actually a bug?}
    real --NO--> intended{Is the intended\nbehaviour?}
    intended --YES--> explain[Explain and close\npoint to docs if needed]
    intended --NO--> open[Keep open for discussion\nRemove 'pending triage' label]
    real --YES--> real2["1. Remove 'pending triage' label\n2. Add related feature label if\napplicable (e.g. 'feat: browser')\n3. Add priority and meta labels (see below)"]
    real2 --> unusable{Does the\nbug make Vitest\nunusable?}
    unusable --YES--> maj{Does the bug\naffect the majority\nof Vitest users?}
    maj --YES--> p5[p5: urgent]
    maj --NO--> p4[p4: important]
    unusable --NO--> workarounds{Are there\nworkarounds for\nthe bug?}
    workarounds --YES--> p2[p2: edge case\nhas workaround]
    workarounds --NO--> p3[p3: minor bug]

Pull Request Review Workflow

flowchart TD
    start{Bug fix\nor\nfeature}
    start --BUG FIX--> strict_bug{"Is a 'strict fix'\ni.e. fixes an obvious\noversight with no\nside effects"}
    start --FEATURE--> feature[- Discuss feature necessity\n- Is this the best way to address the need\n- Review code quality\n- Add feature labels\n- Approve if you feel strongly\nthat the feature is needed]
    feature --> merge
    strict_bug --YES--> strict[- Verify the fix locally\n- Review code quality\n- Require test case if applicable\n- Request changes if necessary]
    strict_bug --NO--> non_strict[- Discuss the potential side\neffects of the fix, e.g.\n- Could it introduce implicit\nbehavior changes in other\ncases?\n- Does it introduce too much\nchanges?]
    non_strict --> label["Add priority labels\n(see issue triaging workflow)"]
    strict --> label
    label --> approve
    approve --> merge["Merge if approved by 2 or\nmore team members\n- Use 'Squash and Merge'\n- Edit commit message to follow\nconvention\n- In commit message body, list\nrelevant issues being fixed\ne.g. 'fix #1234, fix #1235'"]

Notes on Dependencies

Vitest aims to be lightweight, and this includes being aware of the number of npm dependencies and their size.

Think before adding a dependency

Most deps should be added to devDependencies even if they are needed at runtime. Some exceptions are:

  • Type packages. Example: @types/*.
  • Deps that cannot be properly bundled due to binary files.
  • Deps that ships its own types and its type is used in vitest's own public types.

Avoid deps that has large transitive dependencies that results in bloated size compared to the functionality it provides.

If there are libraries that are needed and don't comply with our size requirements, a fork can be tried to reduce its size while we work with them to upstream our changes (see tinypool for example)

Think before adding yet another option

We already have many config options, and we should avoid fixing an issue by adding yet another one. Before adding an option, try to think about:

  • Whether the problem is really worth addressing
  • Whether the problem can be fixed with a smarter default
  • Whether the problem has workaround using existing options
  • Whether the problem can be addressed with a plugin instead