Add a RunOnEventLoop method to modulestest.Runtime

[oleiade]

What?

This Pull Request adds a RunOnEventLoop method to the modulestest.Runtime, to facilitate testing code that should be dispatched to the event loop, such as code that returns promises.

Why?

While writing tests for the #3142, I stumbled upon this code from @mstoykov, with a TODO attached. I thought that as I was about to copy-paste that snippet anyway, I might as well do as instructed in TODO and move the code to the modulestest.Runtime class.

The TODO hinted at potential improvements without detailing that I'd be nonetheless happy to include if necessary 🤞🏻

Checklist

• I have performed a self-review of my code.
• I have added tests for my changes.
• I have run linter locally (make ci-like-lint) and all checks pass.
• I have run tests locally (make tests) and all tests pass.
• I have commented on my code, particularly in hard-to-understand areas.

Related PR(s)/Issue(s)

[codecov-commenter]

Codecov Report

Merging #3181 (4154faf) into master (1b446a4) will increase coverage by 0.01%.
The diff coverage is 80.00%.

❗ Current head 4154faf differs from pull request most recent head 4f152fd. Consider uploading reports for the commit 4f152fd to get more accurate results

@@            Coverage Diff             @@
##           master    #3181      +/-   ##
==========================================
+ Coverage   72.78%   72.80%   +0.01%     
==========================================
  Files         256      256              
  Lines       19697    19703       +6     
==========================================
+ Hits        14337    14344       +7     
+ Misses       4464     4463       -1     
  Partials      896      896              

Flag	Coverage Δ
ubuntu	72.72% <80.00%> (+<0.01%)	⬆️
windows	72.66% <80.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
output/cloud/expv2/output.go	64.77% <0.00%> (ø)
js/modulestest/runtime.go	100.00% <100.00%> (ø)
output/cloud/expv2/hdr.go	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

[olegbespalov]

🚀