--- name: vitest-20a398530e53 description: >- Vitest is a test runner for JavaScript and TypeScript built on Vite, with a Jest-compatible API, built-in mocking, snapshots and code coverage. Use when a user asks to set up or run unit tests in a Vite or Node project, write tests with describe/it/expect, mock modules with vi.mock, add coverage thresholds, configure vitest.config.ts or test projects, migrate from Jest, or upgrade to Vitest 5. license: Apache-2.0 compatibility: "Node.js 22.12+ and Vite 6.4+ (Vitest 5)" metadata: author: terminal-skills version: 1.1.0 category: development repository: https://github.com/vitest-dev/vitest tags: "testing, vite, typescript, mocking, coverage" --- # Vitest — Blazing Fast Unit Testing ## Overview Vitest is the Vite-native testing framework. It runs unit, integration and component tests with native TypeScript support, a Jest-compatible API, built-in mocking, code coverage, snapshot testing and watch mode — reusing Vite's transform pipeline, so tests need no separate compilation step. This skill targets Vitest 5 (released September 2026), which changed several defaults; the Guidelines list what to check when upgrading. ## Instructions ### Installation ```bash npm install -D vitest npm install -D @vitest/coverage-v8 # Coverage npm install -D @vitest/ui # Browser UI npm install -D jsdom # Only for environment: "jsdom" ``` Vitest 5 needs Node.js 22.12+ and Vite 6.4+. Vite is a peer dependency: npm, pnpm and Bun install it automatically, Yarn needs `yarn add -D vitest vite`. Add `.vitest/` (reports and artifacts) and `coverage/` to `.gitignore`. ### Tests ```typescript // src/pricing.test.ts import { describe, it, expect } from "vitest"; import { calculateDiscount, formatPrice } from "./pricing"; describe("calculateDiscount", () => { it("applies percentage discount", () => { expect(calculateDiscount(100, 20)).toBe(80); }); it("never goes below zero", () => { expect(calculateDiscount(10, 200)).toBe(0); }); it.each([ { price: 100, discount: 10, expected: 90 }, { price: 50, discount: 50, expected: 25 }, { price: 200, discount: 0, expected: 200 }, ])("$price with $discount% = $expected", ({ price, discount, expected }) => { expect(calculateDiscount(price, discount)).toBe(expected); }); }); describe("formatPrice", () => { it("formats with currency symbol", () => { expect(formatPrice(29.99, "USD")).toBe("$29.99"); expect(formatPrice(29.99, "EUR")).toBe("€29.99"); }); }); ``` Test files must contain `.test.` or `.spec.` in their name (default `include`: `**/*.{test,spec}.?(c|m)[jt]s?(x)`). ### Mocking ```typescript // src/orders.test.ts import { describe, it, expect, vi } from "vitest"; import { processOrder } from "./orders"; import { sendEmail } from "./email"; import { chargeCard } from "./payments"; // vi.mock is hoisted above the imports — keep it at the top level of the file vi.mock("./email", () => ({ sendEmail: vi.fn().mockResolvedValue({ success: true }), })); vi.mock("./payments", () => ({ chargeCard: vi.fn().mockResolvedValue({ chargeId: "ch_3PqXk2" }), })); describe("processOrder", () => { // No beforeEach(vi.clearAllMocks) needed: Vitest 5 clears call history before every test it("charges card and sends confirmation email", async () => { const order = { userId: "u_481", items: [{ id: "sku_114", qty: 2 }], total: 59.98 }; const result = await processOrder(order); expect(chargeCard).toHaveBeenCalledWith({ amount: 59.98, userId: "u_481" }); expect(sendEmail).toHaveBeenCalledWith( expect.objectContaining({ type: "order_confirmation", userId: "u_481" }), ); expect(result.status).toBe("completed"); }); it("stops on payment failure", async () => { vi.mocked(chargeCard).mockRejectedValueOnce(new Error("Card declined")); await expect(processOrder({ userId: "u_481", items: [], total: 0 })) .rejects.toThrow("Card declined"); expect(sendEmail).not.toHaveBeenCalled(); }); it("spies on a method", () => { const spy = vi.spyOn(console, "log").mockImplementation(() => {}); console.log("order shipped"); expect(spy).toHaveBeenCalledWith("order shipped"); }); it("controls timers", () => { vi.useFakeTimers(); const callback = vi.fn(); setTimeout(callback, 5000); vi.advanceTimersByTime(5000); expect(callback).toHaveBeenCalled(); vi.useRealTimers(); }); }); ``` To keep the real implementation and only record calls, pass `{ spy: true }` instead of a factory: `vi.mock(import("./payments"), { spy: true })`. ### Configuration ```typescript // vitest.config.ts import { defineConfig } from "vitest/config"; export default defineConfig({ test: { globals: true, // No need to import describe/it/expect environment: "node", // Or "jsdom" / "happy-dom" for browser APIs coverage: { provider: "v8", reporter: ["text", "html", "lcov"], include: ["src/**/*.ts"], // Also report files no test imports thresholds: { lines: 80, branches: 75, functions: 80 }, }, include: ["**/*.{test,spec}.{ts,tsx}"], setupFiles: ["./test/setup.ts"], // The file must exist; drop the line if there is none }, }); ``` Vitest also reads `test` from an existing `vite.config.ts`. With `globals: true`, add `"types": ["vitest/globals"]` to `compilerOptions` in `tsconfig.json`. A single file can switch environment with a `// @vitest-environment jsdom` comment at the top of the file. Several configurations in one run (monorepo packages, node + DOM tests) are declared as `projects` in the root config: ```typescript // vitest.config.ts import { defineConfig } from "vitest/config"; export default defineConfig({ test: { coverage: { provider: "v8", include: ["src/**/*.ts"] }, // root-only option projects: [ { test: { name: "unit", include: ["src/**/*.test.ts"], environment: "node" } }, { test: { name: "dom", include: ["src/**/*.dom.test.tsx"], environment: "jsdom" } }, "packages/*", // every folder in packages/ is a project ], }, }); ``` ### Running ```bash npx vitest # Watch mode; single run in CI or without a TTY npx vitest run # Single run (CI) npx vitest run --coverage # With coverage, fails below thresholds npx vitest --ui # Browser UI — open the printed URL, it carries a token npx vitest run src/pricing.test.ts # Files whose path contains the filter npx vitest run -t "applies percentage" # Tests whose full name matches npx vitest run --project unit # One project npx vitest related src/pricing.ts --run # Tests that import the given source files npx vitest run --changed # Tests affected by uncommitted changes npx vitest run --reporter=junit # Writes .vitest/junit/output.xml ``` ## Examples ### Example 1: Add tests and a coverage gate to a TypeScript project User: "Set up Vitest for our pricing module and make CI fail under 80% line coverage." ```bash npm install -D vitest @vitest/coverage-v8 npm pkg set scripts.test="vitest" scripts.test:ci="vitest run --coverage" npm run test:ci ``` With the two test files and the first configuration above (and an existing `test/setup.ts`), the mocked `email.ts` and `payments.ts` never execute, so the totals fall under the threshold and the command exits with code 1: ```text Test Files 2 passed (2) Tests 10 passed (10) % Coverage report from v8 -------------|---------|----------|---------|---------|------------------- File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s -------------|---------|----------|---------|---------|------------------- All files | 71.42 | 100 | 60 | 71.42 | email.ts | 0 | 100 | 0 | 0 | 1 payments.ts | 0 | 100 | 0 | 0 | 1 -------------|---------|----------|---------|---------|------------------- ERROR: Coverage for lines (71.42%) does not meet global threshold (80%) ERROR: Coverage for functions (60%) does not meet global threshold (80%) ``` The HTML report is written to `coverage/index.html`. ### Example 2: Upgrade a monorepo from Vitest 3 to Vitest 5 User: "After bumping vitest to 5 our workspace tests are gone and one file crashes with a vi.mock error." 1. `vitest.workspace.ts` is no longer read, and a `test.workspace` key throws "The `test.workspace` option was removed in Vitest 4". Move its entries into `test.projects` (see Configuration) and delete the file. 2. Move every `vi.mock` / `vi.hoisted` call out of `describe` and `test` callbacks to the top level of the file. Vitest 5 fails the file otherwise: ```text Error: 1 call in "src/orders.test.ts" was defined outside of the module's top level scope: - vi.mock("./email") at src/orders.test.ts:2:28 ``` 3. Run one project and read the full report: ```bash npx vitest run --project unit --reporter=default ``` ```text ✓ |unit| src/orders.test.ts (4 tests) 4ms ✓ |unit| src/pricing.test.ts (6 tests) 10ms Test Files 2 passed (2) Tests 10 passed (10) ``` 4. Assertions that counted calls made in an earlier test or in `beforeAll` now see zero calls (`clearMocks` is on). Fix the test, or set `test.clearMocks: false` to restore the old behavior. ## Guidelines 1. **Vite-powered** — Uses Vite's transform; TypeScript, JSX, ESM work without config; instant re-runs in watch mode 2. **Jest-compatible** — Same `describe`/`it`/`expect` API; replace `jest.fn`/`jest.mock` with `vi.fn`/`vi.mock` when migrating 3. **Native TypeScript** — No ts-jest, no babel; Vite handles transforms. Tests run without type checking, so keep `tsc --noEmit` in CI 4. **vi.mock() is hoisted** — It runs before imports, so a factory cannot use variables declared below it; create those with `vi.hoisted()`. Use `vi.doMock()` when a mock must be registered later, inside a test 5. **Mock history resets by itself** — Since Vitest 5 `clearMocks` defaults to `true`: call counts are cleared before each test, implementations stay. `mockReset` and `restoreMocks` are still opt-in 6. **In-source testing** — Tests inside `if (import.meta.vitest)` blocks run once `test.includeSource` lists the files; add `define: { "import.meta.vitest": "undefined" }` to the build config so bundlers drop them from production 7. **Projects, not workspaces** — `test.projects` replaced `vitest.workspace.ts`. Inline projects inherit the root config by default in Vitest 5 (`extends: false` opts out); `coverage` and `reporters` can only be set at the root 8. **Coverage counts imported files only** — Set `coverage.include` to see untested files. In Vitest 5 a pattern without wildcards (`"src"`) is treated as a directory, and glob thresholds need their own `perFile` 9. **Reports go to `.vitest/`** — The `json` and `junit` reporters write `.vitest/json/output.json` and `.vitest/junit/output.xml` instead of stdout unless `outputFile` is set 10. **Quiet output under AI agents** — When Vitest detects a coding agent it switches to the `minimal` reporter, which prints only failures and the totals. Pass `--reporter=default` (or `verbose`) to see every file 11. **Config lookup** — Vitest 5 no longer searches parent directories for a config file; run from the project root or pass `--config ../vitest.config.ts` 12. **Not an end-to-end tool** — For full user flows across pages use Playwright or Cypress. Component tests that need a real browser can use Browser Mode (`npx vitest init browser`) --- Source attribution: terminal-skills Original project: https://github.com/TerminalSkills/skills/blob/8a9852d489f274538be9bf1c9121aeb403750b1c/skills/vitest/SKILL.md License: Apache-2.0 License information: https://www.apache.org/licenses/LICENSE-2.0 Original upstream instructions; downloaded from Mega AI Hub. ## Upstream license notice Apache License Version 2.0, January 2004 http://www.apache.org/licenses/ TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 1. Definitions. "License" shall mean the terms and conditions for use, reproduction, and distribution as defined by Sections 1 through 9 of this document. "Licensor" shall mean the copyright owner or entity authorized by the copyright owner that is granting the License. "Legal Entity" shall mean the union of the acting entity and all other entities that control, are controlled by, or are under common control with that entity. For the purposes of this definition, "control" means (i) the power, direct or indirect, to cause the direction or management of such entity, whether by contract or otherwise, or (ii) ownership of fifty percent (50%) or more of the outstanding shares, or (iii) beneficial ownership of such entity. "You" (or "Your") shall mean an individual or Legal Entity exercising permissions granted by this License. "Source" form shall mean the preferred form for making modifications, including but not limited to software source code, documentation source, and configuration files. "Object" form shall mean any form resulting from mechanical transformation or translation of a Source form, including but not limited to compiled object code, generated documentation, and conversions to other media types. "Work" shall mean the work of authorship, whether in Source or Object form, made available under the License, as indicated by a copyright notice that is included in or attached to the work (an example is provided in the Appendix below). "Derivative Works" shall mean any work, whether in Source or Object form, that is based on (or derived from) the Work and for which the editorial revisions, annotations, elaborations, or other modifications represent, as a whole, an original work of authorship. For the purposes of this License, Derivative Works shall not include works that remain separable from, or merely link (or bind by name) to the interfaces of, the Work and Derivative Works thereof. "Contribution" shall mean any work of authorship, including the original version of the Work and any modifications or additions to that Work or Derivative Works thereof, that is intentionally submitted to the Licensor for inclusion in the Work by the copyright owner or by an individual or Legal Entity authorized to submit on behalf of the copyright owner. For the purposes of this definition, "submitted" means any form of electronic, verbal, or written communication sent to the Licensor or its representatives, including but not limited to communication on electronic mailing lists, source code control systems, and issue tracking systems that are managed by, or on behalf of, the Licensor for the purpose of discussing and improving the Work, but excluding communication that is conspicuously marked or otherwise designated in writing by the copyright owner as "Not a Contribution." "Contributor" shall mean Licensor and any individual or Legal Entity on behalf of whom a Contribution has been received by the Licensor and subsequently incorporated within the Work. 2. Grant of Copyright License. Subject to the terms and conditions of this License, each Contributor hereby grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare Derivative Works of, publicly display, publicly perform, sublicense, and distribute the Work and such Derivative Works in Source or Object form. 3. Grant of Patent License. Subject to the terms and conditions of this License, each Contributor hereby grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable (except as stated in this section) patent license to make, have made, use, offer to sell, sell, import, and otherwise transfer the Work, where such license applies only to those patent claims licensable by such Contributor that are necessarily infringed by their Contribution(s) alone or by combination of their Contribution(s) with the Work to which such Contribution(s) was submitted. If You institute patent litigation against any entity (including a cross-claim or counterclaim in a lawsuit) alleging that the Work or a Contribution incorporated within the Work constitutes direct or contributory patent infringement, then any patent licenses granted to You under this License for that Work shall terminate as of the date such litigation is filed. 4. Redistribution. You may reproduce and distribute copies of the Work or Derivative Works thereof in any medium, with or without modifications, and in Source or Object form, provided that You meet the following conditions: (a) You must give any other recipients of the Work or Derivative Works a copy of this License; and (b) You must cause any modified files to carry prominent notices stating that You changed the files; and (c) You must retain, in the Source form of any Derivative Works that You distribute, all copyright, patent, trademark, and attribution notices from the Source form of the Work, excluding those notices that do not pertain to any part of the Derivative Works; and (d) If the Work includes a "NOTICE" text file as part of its distribution, then any Derivative Works that You distribute must include a readable copy of the attribution notices contained within such NOTICE file, excluding any notices that do not pertain to any part of the Derivative Works, in at least one of the following places: within a NOTICE text file distributed as part of the Derivative Works; within the Source form or documentation, if provided along with the Derivative Works; or, within a display generated by the Derivative Works, if and wherever such third-party notices normally appear. The contents of the NOTICE file are for informational purposes only and do not modify the License. You may add Your own attribution notices within Derivative Works that You distribute, alongside or as an addendum to the NOTICE text from the Work, provided that such additional attribution notices cannot be construed as modifying the License. You may add Your own copyright statement to Your modifications and may provide additional or different license terms and conditions for use, reproduction, or distribution of Your modifications, or for any such Derivative Works as a whole, provided Your use, reproduction, and distribution of the Work otherwise complies with the conditions stated in this License. 5. Submission of Contributions. Unless You explicitly state otherwise, any Contribution intentionally submitted for inclusion in the Work by You to the Licensor shall be under the terms and conditions of this License, without any additional terms or conditions. Notwithstanding the above, nothing herein shall supersede or modify the terms of any separate license agreement you may have executed with Licensor regarding such Contributions. 6. Trademarks. This License does not grant permission to use the trade names, trademarks, service marks, or product names of the Licensor, except as required for reasonable and customary use in describing the origin of the Work and reproducing the content of the NOTICE file. 7. Disclaimer of Warranty. Unless required by applicable law or agreed to in writing, Licensor provides the Work (and each Contributor provides its Contributions) on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. You are solely responsible for determining the appropriateness of using or redistributing the Work and assume any risks associated with Your exercise of permissions under this License. 8. Limitation of Liability. In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall any Contributor be liable to You for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising as a result of this License or out of the use or inability to use the Work (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if such Contributor has been advised of the possibility of such damages. 9. Accepting Warranty or Additional Liability. While redistributing the Work or Derivative Works thereof, You may choose to offer, and charge a fee for, acceptance of support, warranty, indemnity, or other liability obligations and/or rights consistent with this License. However, in accepting such obligations, You may act only on Your own behalf and on Your sole responsibility, not on behalf of any other Contributor, and only if You agree to indemnify, defend, and hold each Contributor harmless for any liability incurred by, or claims asserted against, such Contributor by reason of your accepting any such warranty or additional liability. END OF TERMS AND CONDITIONS Copyright 2025 Terminal Skills Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. # Mega AI Hub resource metadata Creator / publisher: terminal-skills Original project: https://github.com/TerminalSkills/skills/blob/8a9852d489f274538be9bf1c9121aeb403750b1c/skills/vitest/SKILL.md Attribution basis: Source repository record Fields of work: Development & Engineering Roles: QA / Test Engineer, Backend Developer, Frontend Developer Specialties: Frontend, Stripe, API, Testing Tools: Playwright Country applicability: Country not specified Classification basis: Source category, role and specialization labels Instruction SHA-256: 51c81107991c4141f88a07ada9263a85f7151afd856ab28fea6f10e0d3d41398