Experimental next/jest config helper

[timneutkens]

Closes #31222

Expands the scope of next/jest to the config file itself, this allows for:

• Auto mocking of .css, .module.css (and their scss variants), and image imports
• Automatically sets up transform using SWC
• Loading .env (and all variants) into process.env
• Ignores node_modules from test resolving and transforms
• Ignoring .next from test resolving
• Loads next.config.js for flags that enable experimental SWC transforms
• Prepares for tsconfig/jsconfig paths, currently commented out as there's a bug with the handling of "paths" in SWC that causes .module.css to be transformed into .module.

Example usage, I don't feel strongly about the API, we might want to change it a bit:

// Usage in jest.config.js
const nextJest = require('next/jest');
// Optionally provide path to Next.js app which will enable loading next.config.js and .env files
const createJestConfig = nextJest({ dir })
// Any custom config you want to pass to Jest
const customJestConfig = {
    setupFilesAfterEnv: ['<rootDir>/jest.setup.js'],
}
// createJestConfig is exported in this way to ensure that next/jest can load the Next.js config which is async
module.exports = createJestConfig(customJestConfig)

Bug

• Related issues linked using fixes #number
• Integration tests added
• Errors have helpful link attached, see contributing.md

Feature

• Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
• Related issues linked using fixes #number
• Integration tests added
• Documentation added
• Telemetry added. In case of a feature if it's used or not.
• Errors have helpful link attached, see contributing.md

Documentation / Examples

• Make sure the linting passes by running yarn lint

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	timneutkens/next.js add/jest-config	Change
buildDuration	22.4s	22.5s	⚠️ +124ms
buildDurationCached	4.2s	4.2s	⚠️ +33ms
nodeModulesSize	334 MB	334 MB	⚠️ +13.1 kB

Page Load Tests Overall increase ✓

	vercel/next.js canary	timneutkens/next.js add/jest-config	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.813	3.773	-0.04
/ avg req/sec	655.69	662.67	+6.98
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	2.034	2.018	-0.02
/error-in-render avg req/sec	1229.2	1238.87	+9.67

Client Bundles (main, webpack, commons)

	vercel/next.js canary	timneutkens/next.js add/jest-config	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.2 kB	42.2 kB	✓
main-HASH.js gzip	28.2 kB	28.2 kB	✓
webpack-HASH.js gzip	1.45 kB	1.45 kB	✓
Overall change	72.1 kB	72.1 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	timneutkens/next.js add/jest-config	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	timneutkens/next.js add/jest-config	Change
_app-HASH.js gzip	1.37 kB	1.37 kB	✓
_error-HASH.js gzip	194 B	194 B	✓
amp-HASH.js gzip	312 B	312 B	✓
css-HASH.js gzip	327 B	327 B	✓
dynamic-HASH.js gzip	2.38 kB	2.38 kB	✓
head-HASH.js gzip	350 B	350 B	✓
hooks-HASH.js gzip	635 B	635 B	✓
image-HASH.js gzip	4.44 kB	4.44 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	1.87 kB	1.87 kB	✓
routerDirect..HASH.js gzip	321 B	321 B	✓
script-HASH.js gzip	383 B	383 B	✓
withRouter-HASH.js gzip	318 B	318 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	13.3 kB	13.3 kB	✓

Client Build Manifests

	vercel/next.js canary	timneutkens/next.js add/jest-config	Change
_buildManifest.js gzip	460 B	460 B	✓
Overall change	460 B	460 B	✓

Rendered Page Sizes

	vercel/next.js canary	timneutkens/next.js add/jest-config	Change
index.html gzip	522 B	522 B	✓
link.html gzip	535 B	535 B	✓
withRouter.html gzip	516 B	516 B	✓
Overall change	1.57 kB	1.57 kB	✓

---

Default Build with SWC (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	timneutkens/next.js add/jest-config	Change
buildDuration	24.5s	24.5s	⚠️ +9ms
buildDurationCached	4.5s	4.5s	⚠️ +41ms
nodeModulesSize	334 MB	334 MB	⚠️ +13.1 kB

Page Load Tests Overall increase ✓

	vercel/next.js canary	timneutkens/next.js add/jest-config	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.967	3.74	-0.23
/ avg req/sec	630.27	668.4	+38.13
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	2.048	2.058	⚠️ +0.01
/error-in-render avg req/sec	1220.86	1214.66	⚠️ -6.2

Client Bundles (main, webpack, commons)

	vercel/next.js canary	timneutkens/next.js add/jest-config	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.3 kB	42.3 kB	✓
main-HASH.js gzip	28.4 kB	28.4 kB	✓
webpack-HASH.js gzip	1.43 kB	1.43 kB	✓
Overall change	72.4 kB	72.4 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	timneutkens/next.js add/jest-config	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	timneutkens/next.js add/jest-config	Change
_app-HASH.js gzip	1.35 kB	1.35 kB	✓
_error-HASH.js gzip	180 B	180 B	✓
amp-HASH.js gzip	305 B	305 B	✓
css-HASH.js gzip	321 B	321 B	✓
dynamic-HASH.js gzip	2.38 kB	2.38 kB	✓
head-HASH.js gzip	342 B	342 B	✓
hooks-HASH.js gzip	622 B	622 B	✓
image-HASH.js gzip	4.46 kB	4.46 kB	✓
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	1.91 kB	1.91 kB	✓
routerDirect..HASH.js gzip	314 B	314 B	✓
script-HASH.js gzip	375 B	375 B	✓
withRouter-HASH.js gzip	309 B	309 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	13.2 kB	13.2 kB	✓

Client Build Manifests

	vercel/next.js canary	timneutkens/next.js add/jest-config	Change
_buildManifest.js gzip	459 B	459 B	✓
Overall change	459 B	459 B	✓

Rendered Page Sizes

	vercel/next.js canary	timneutkens/next.js add/jest-config	Change
index.html gzip	522 B	522 B	✓
link.html gzip	534 B	534 B	✓
withRouter.html gzip	515 B	515 B	✓
Overall change	1.57 kB	1.57 kB	✓

Commit: 179ddce