Ensure mjs files are transformed with jest

[ijjk]

This ensures we handle .mjs files in our next/jest config and also removes the extra extension check in our jest-transformer

Bug

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

Fixes: #34182

[timneutkens]

Would it make sense to add the tests to test/production/next/jest/index.test.ts instead? That way the use the same isolation as the rest of the integration test suite

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall decrease ✓

	vercel/next.js canary	ijjk/next.js fix/jest-transform-exts	Change
buildDuration	15s	14.9s	-132ms
buildDurationCached	6.1s	5.8s	-344ms
nodeModulesSize	372 MB	372 MB	-174 B

Page Load Tests Overall increase ✓

	vercel/next.js canary	ijjk/next.js fix/jest-transform-exts	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.935	2.984	⚠️ +0.05
/ avg req/sec	851.64	837.83	⚠️ -13.81
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.321	1.304	-0.02
/error-in-render avg req/sec	1892.51	1916.82	+24.31

Client Bundles (main, webpack)

	vercel/next.js canary	ijjk/next.js fix/jest-transform-exts	Change
925.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42 kB	42 kB	✓
main-HASH.js gzip	27.9 kB	27.9 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	71.6 kB	71.6 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	ijjk/next.js fix/jest-transform-exts	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	ijjk/next.js fix/jest-transform-exts	Change
_app-HASH.js gzip	1.36 kB	1.36 kB	✓
_error-HASH.js gzip	192 B	192 B	✓
amp-HASH.js gzip	309 B	309 B	✓
css-HASH.js gzip	327 B	327 B	✓
dynamic-HASH.js gzip	2.57 kB	2.57 kB	✓
head-HASH.js gzip	351 B	351 B	✓
hooks-HASH.js gzip	920 B	920 B	✓
image-HASH.js gzip	5.09 kB	5.09 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	2.26 kB	2.26 kB	✓
routerDirect..HASH.js gzip	320 B	320 B	✓
script-HASH.js gzip	387 B	387 B	✓
withRouter-HASH.js gzip	319 B	319 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	14.8 kB	14.8 kB	✓

Client Build Manifests

	vercel/next.js canary	ijjk/next.js fix/jest-transform-exts	Change
_buildManifest.js gzip	460 B	460 B	✓
Overall change	460 B	460 B	✓

Rendered Page Sizes

	vercel/next.js canary	ijjk/next.js fix/jest-transform-exts	Change
index.html gzip	531 B	531 B	✓
link.html gzip	546 B	546 B	✓
withRouter.html gzip	526 B	526 B	✓
Overall change	1.6 kB	1.6 kB	✓

---

Default Build with SWC (Increase detected ⚠️)

General Overall decrease ✓

	vercel/next.js canary	ijjk/next.js fix/jest-transform-exts	Change
buildDuration	17.8s	18.2s	⚠️ +411ms
buildDurationCached	6.1s	5.7s	-328ms
nodeModulesSize	372 MB	372 MB	-174 B

Page Load Tests Overall increase ✓

	vercel/next.js canary	ijjk/next.js fix/jest-transform-exts	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.844	2.999	⚠️ +0.16
/ avg req/sec	879.15	833.74	⚠️ -45.41
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.33	1.265	-0.07
/error-in-render avg req/sec	1880.25	1976.08	+95.83

Client Bundles (main, webpack)

	vercel/next.js canary	ijjk/next.js fix/jest-transform-exts	Change
925.HASH.js gzip	178 B	178 B	✓
framework-HASH.js gzip	42.3 kB	42.3 kB	✓
main-HASH.js gzip	28.2 kB	28.2 kB	✓
webpack-HASH.js gzip	1.45 kB	1.45 kB	✓
Overall change	72.2 kB	72.2 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	ijjk/next.js fix/jest-transform-exts	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	ijjk/next.js fix/jest-transform-exts	Change
_app-HASH.js gzip	1.35 kB	1.35 kB	✓
_error-HASH.js gzip	179 B	179 B	✓
amp-HASH.js gzip	313 B	313 B	✓
css-HASH.js gzip	324 B	324 B	✓
dynamic-HASH.js gzip	2.56 kB	2.56 kB	✓
head-HASH.js gzip	351 B	351 B	✓
hooks-HASH.js gzip	921 B	921 B	✓
image-HASH.js gzip	5.23 kB	5.23 kB	✓
index-HASH.js gzip	261 B	261 B	✓
link-HASH.js gzip	2.33 kB	2.33 kB	✓
routerDirect..HASH.js gzip	322 B	322 B	✓
script-HASH.js gzip	388 B	388 B	✓
withRouter-HASH.js gzip	317 B	317 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	15 kB	15 kB	✓

Client Build Manifests

	vercel/next.js canary	ijjk/next.js fix/jest-transform-exts	Change
_buildManifest.js gzip	459 B	459 B	✓
Overall change	459 B	459 B	✓

Rendered Page Sizes

	vercel/next.js canary	ijjk/next.js fix/jest-transform-exts	Change
index.html gzip	530 B	530 B	✓
link.html gzip	545 B	545 B	✓
withRouter.html gzip	526 B	526 B	✓
Overall change	1.6 kB	1.6 kB	✓

Commit: dad8ffe