test: add cache testing

[tsctx]

No description provided.

[codecov-commenter]

Codecov Report

Attention: 176 lines in your changes are missing coverage. Please review.

Comparison is base (e39a632) 85.54% compared to head (fc5398f) 87.28%.
Report is 225 commits behind head on main.

Files	Patch %	Lines
lib/fetch/index.js	67.29%	52 Missing ⚠️
lib/fetch/util.js	37.17%	49 Missing ⚠️
lib/handler/RetryHandler.js	74.35%	30 Missing ⚠️
lib/cache/cache.js	65.71%	12 Missing ⚠️
lib/core/diagnostics.js	84.74%	9 Missing ⚠️
lib/api/readable.js	88.88%	5 Missing ⚠️
lib/fetch/headers.js	90.19%	5 Missing ⚠️
lib/client.js	95.23%	3 Missing ⚠️
lib/compat/dispatcher-weakref.js	57.14%	3 Missing ⚠️
lib/core/util.js	95.65%	2 Missing ⚠️
... and 5 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2623      +/-   ##
==========================================
+ Coverage   85.54%   87.28%   +1.73%     
==========================================
  Files          76       81       +5     
  Lines        6858     7293     +435     
==========================================
+ Hits         5867     6366     +499     
+ Misses        991      927      -64     

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[mcollina]

lgtm

[KhafraDev]

I'm pretty sure Every test here is already covered by WPTs. There is no reason to add these tests.

[tsctx]

@KhafraDev #2612 (comment)

[KhafraDev]

I think Matteo meant was that a test specifically for accessing the signal was needed, not that we need to duplicate the tests