feat(learn): clean up code sample & update/correct time mocking section

[JakobJingleheimer]

Resolves nodejs/node#62081
Resolves nodejs/node#62141

[vercel]

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Project	Deployment	Actions	Updated (UTC)
nodejs-org	Ready	Preview	Mar 8, 2026 1:20pm

[github-actions]

👋 Codeowner Review Request

The following codeowners have been identified for the changed files:

Team reviewers: @nodejs/test_runner

Please review the changes when you have a chance. Thank you! 🙏

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.10%. Comparing base (5fc6baa) to head (51af870).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8707      +/-   ##
==========================================
+ Coverage   75.09%   75.10%   +0.01%     
==========================================
  Files         104      104              
  Lines        9161     9161              
  Branches      315      315              
==========================================
+ Hits         6879     6880       +1     
+ Misses       2280     2279       -1     
  Partials        2        2              

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[Copilot]

Pull request overview

Updates the Node.js test-runner “Mocking” learning page to correct the time-mocking guidance and simplify the accompanying examples (per linked Node.js issue/PR).

Changes:

• Refactors the module-mocking example to set up mock.module() and perform the consumer import in-sequence within the describe block.
• Fixes the time-mocking example to enable mock.timers before importing the module under test, and adds an explicit explanation of why a dynamic import is required.

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[github-actions]

📦 Build Size Comparison

Summary

Metric	Value
Old Total Size	3.51 MB
New Total Size	3.51 MB
Delta	0 B (0.00%)

Changes

➕ Added Assets (1)

Name	Size
.next/static/chunks/ea489969291ac20a.js	208.15 KB

➖ Removed Assets (1)

Name	Size
.next/static/chunks/e30c75c2554188d5.js	208.15 KB