Fix side effects in router-is-ready tests

[devknoll]

Fixes the failing react@experimental tests.

[ijjk]

Stats from current PR

Default Server Mode (Increase detected ⚠️)

General

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
buildDuration	16.1s	16s	-74ms
buildDurationCached	5.3s	4.8s	-451ms
nodeModulesSize	46.6 MB	46.6 MB	✓

Page Load Tests Overall increase ✓

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.732	2.789	⚠️ +0.06
/ avg req/sec	915.1	896.25	⚠️ -18.85
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.609	1.573	-0.04
/error-in-render avg req/sec	1553.89	1589.19	+35.3

Client Bundles (main, webpack, commons)

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
597-HASH.js gzip	13.3 kB	13.3 kB	✓
778-HASH.js gzip	7.12 kB	7.12 kB	✓
framework-HASH.js gzip	39.3 kB	39.3 kB	✓
main-HASH.js gzip	151 B	151 B	✓
webpack-HASH.js gzip	993 B	993 B	✓
Overall change	60.8 kB	60.8 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
polyfills-HASH.js gzip	31.1 kB	31.1 kB	✓
Overall change	31.1 kB	31.1 kB	✓

Client Pages

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
_app-HASH.js gzip	1.3 kB	1.3 kB	✓
_error-HASH.js gzip	3.68 kB	3.68 kB	✓
amp-HASH.js gzip	558 B	558 B	✓
css-HASH.js gzip	363 B	363 B	✓
hooks-HASH.js gzip	924 B	924 B	✓
index-HASH.js gzip	243 B	243 B	✓
link-HASH.js gzip	1.66 kB	1.66 kB	✓
routerDirect..HASH.js gzip	336 B	336 B	✓
withRouter-HASH.js gzip	334 B	334 B	✓
99a142a5cfae..804.css gzip	125 B	125 B	✓
Overall change	9.52 kB	9.52 kB	✓

Client Build Manifests

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
_buildManifest.js gzip	390 B	390 B	✓
Overall change	390 B	390 B	✓

Rendered Page Sizes

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
index.html gzip	609 B	609 B	✓
link.html gzip	615 B	615 B	✓
withRouter.html gzip	605 B	605 B	✓
Overall change	1.83 kB	1.83 kB	✓

---

Serverless Mode

General

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
buildDuration	19.8s	19.9s	⚠️ +83ms
buildDurationCached	7.3s	7.4s	⚠️ +139ms
nodeModulesSize	46.6 MB	46.6 MB	✓

Client Bundles (main, webpack, commons)

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
597-HASH.js gzip	13.3 kB	13.3 kB	✓
778-HASH.js gzip	7.12 kB	7.12 kB	✓
framework-HASH.js gzip	39.3 kB	39.3 kB	✓
main-HASH.js gzip	151 B	151 B	✓
webpack-HASH.js gzip	993 B	993 B	✓
Overall change	60.8 kB	60.8 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
polyfills-HASH.js gzip	31.1 kB	31.1 kB	✓
Overall change	31.1 kB	31.1 kB	✓

Client Pages

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
_app-HASH.js gzip	1.3 kB	1.3 kB	✓
_error-HASH.js gzip	3.68 kB	3.68 kB	✓
amp-HASH.js gzip	558 B	558 B	✓
css-HASH.js gzip	363 B	363 B	✓
hooks-HASH.js gzip	924 B	924 B	✓
index-HASH.js gzip	243 B	243 B	✓
link-HASH.js gzip	1.66 kB	1.66 kB	✓
routerDirect..HASH.js gzip	336 B	336 B	✓
withRouter-HASH.js gzip	334 B	334 B	✓
99a142a5cfae..804.css gzip	125 B	125 B	✓
Overall change	9.52 kB	9.52 kB	✓

Client Build Manifests

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
_buildManifest.js gzip	390 B	390 B	✓
Overall change	390 B	390 B	✓

Serverless bundles

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
_error.js	1.39 MB	1.39 MB	✓
404.html	2.76 kB	2.76 kB	✓
500.html	2.75 kB	2.75 kB	✓
amp.amp.html	10.8 kB	10.8 kB	✓
amp.html	1.96 kB	1.96 kB	✓
css.html	2.13 kB	2.13 kB	✓
hooks.html	2.01 kB	2.01 kB	✓
index.js	1.39 MB	1.39 MB	✓
link.js	1.45 MB	1.45 MB	⚠️ +2 B
routerDirect.js	1.44 MB	1.44 MB	✓
withRouter.js	1.44 MB	1.44 MB	-2 B
Overall change	7.15 MB	7.15 MB	✓

---

Webpack 4 Mode (Decrease detected ✓)

General

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
buildDuration	13.4s	13.3s	-125ms
buildDurationCached	5.6s	5.8s	⚠️ +189ms
nodeModulesSize	46.6 MB	46.6 MB	✓

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.747	2.695	-0.05
/ avg req/sec	910.08	927.66	+17.58
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.545	1.609	⚠️ +0.06
/error-in-render avg req/sec	1618.37	1554.05	⚠️ -64.32

Client Bundles (main, webpack, commons)

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
677f882d2ed8..HASH.js gzip	13.4 kB	13.4 kB	✓
framework.HASH.js gzip	39 kB	39 kB	✓
main-HASH.js gzip	7.2 kB	7.2 kB	✓
webpack-HASH.js gzip	751 B	751 B	✓
Overall change	60.3 kB	60.3 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
polyfills-HASH.js gzip	31.3 kB	31.3 kB	✓
Overall change	31.3 kB	31.3 kB	✓

Client Pages

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
_app-HASH.js gzip	1.28 kB	1.28 kB	✓
_error-HASH.js gzip	3.71 kB	3.71 kB	✓
amp-HASH.js gzip	536 B	536 B	✓
css-HASH.js gzip	339 B	339 B	✓
hooks-HASH.js gzip	887 B	887 B	✓
index-HASH.js gzip	227 B	227 B	✓
link-HASH.js gzip	1.65 kB	1.65 kB	✓
routerDirect..HASH.js gzip	303 B	303 B	✓
withRouter-HASH.js gzip	302 B	302 B	✓
21c68fa65a48..217.css gzip	125 B	125 B	✓
Overall change	9.36 kB	9.36 kB	✓

Client Build Manifests

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
_buildManifest.js gzip	419 B	419 B	✓
Overall change	419 B	419 B	✓

Rendered Page Sizes

	vercel/next.js canary	azukaru/next.js fix-test-side-effects	Change
index.html gzip	612 B	612 B	✓
link.html gzip	620 B	620 B	✓
withRouter.html gzip	605 B	605 B	✓
Overall change	1.84 kB	1.84 kB	✓

Commit: ab68b47