misc: convert webpack-preprocessor tests to vitest

[AtofStryker]

• Closes N/A

Additional details

Converts the tests in @cypress/webpack-preprocessor from mocha to vitest. Because this is still a CommonJS module that relies on require() to source the TypeScript location for the consuming user, I needed to introduce mock-require and refactored this code into get-typescript to test this functionality separately. proxyquire isn't an option here as I cannot get it to run in the vitest context (see vitest-dev/vitest#3134). This is only temporary until we move to ESM in this module or replace it.

I also merged the helpers file into the e2e.spec.ts as its the only file that is using this.

Steps to test

How has the user experience changed?

PR Tasks

• Have tests been added/updated?
• Has a PR for user-facing changes been opened in cypress-documentation?
• Have API changes been updated in the type definitions?

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Note

Migrates @cypress/webpack-preprocessor tests from Mocha to Vitest, adds a get-typescript helper and refactors TS overrides, updates configs/scripts and minor types/ESM tweaks.

• npm/webpack-preprocessor:
  • Tests → Vitest:
    • Convert unit/e2e tests to Vitest (test/unit/*.spec.ts, test/e2e/*.spec.ts), replace Chai/Sinon/SnapShot with Vitest APIs and snapshots; remove legacy Mocha tests/helpers.
    • Add vitest.config.ts and update snapshots (__snapshots__/compilation.spec.ts.snap).
  • New utility: Add lib/get-typescript.ts and use it in lib/typescript-overrides.ts for resolving the project TypeScript; update tests for it.
  • Preprocessor tweaks:
    • Make WebpackPreprocessorFn options optional; keep CJS export with note for future ESM.
    • Minor cleanup in error handling/types; no functional changes to bundling.
  • Config/Scripts:
    • Update package.json scripts to run Vitest; switch test runner script to TS (scripts/test-webpack-5.ts) and tsx execution; remove Mocha/Chai/Sinon deps; add vitest, strip-ansi, mock-require, TS v5.
    • Convert cypress.config.ts to ESM import/export and simplify preprocessor wiring.
• Docs:
  • Update guides/esm-migration.md checklist to mark npm/webpack-preprocessor as completed in Phase 2.

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[cypress]

cypress    Run #67208

Run Properties:   Failed #67208  •  96651221e1: chore: fix unit tests

Project	cypress
Branch Review	chore/webpack-preprocessor-vitest
Run status	Failed #67208
Run duration	17m 11s
Commit	96651221e1: chore: fix unit tests
Committer	Bill Glesias
View all properties for this run ↗︎

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Test results
Failures	1
Flaky	2
Pending	132
Skipped	0
Passing	6245
View all changes introduced in this branch ↗︎

UI Coverage  38.03%
Untested elements	132
Tested elements	81

Accessibility  97.39%
Failed rules	3 critical   7 serious   1 moderate   1 minor
Failed elements	62

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Tests for review

  cypress/e2e/commands/files.cy.js • 1 failed test • 5x-driver-firefox

View Output

Test		Artifacts
src/cy/commands/files > #readFile > retries to read when ENOENT		</td> </tr></table>   commands/net_stubbing.cy.ts • 1 flaky test • 5x-driver-firefox View Output Test Artifacts ... > stops waiting when an xhr request is canceled </td> </tr></table>   issues/28527.cy.ts • 1 flaky test • 5x-driver-firefox View Output Test Artifacts issue 28527 > fails and then retries and verifies about:blank is not displayed Screenshots

[cursor]

Bug: WriteStream.write: missing return value breaks backpressure

The stdio.write override doesn't return a value when passThrough is falsy, but Node.js WriteStream.write() must return a boolean indicating whether the write was successful. This can cause issues with backpressure handling and may break code that checks the return value.

 

[AtofStryker]

this isn't relevant