test: add e2e test for WEBPACK_SERVE env variable

[snitin315]

• This is a bugfix
• This is a feature
• This is a code refactor
• This is a test update
• This is a docs update
• This is a metadata update

For Bugs and Features; did you add new tests?

refactor

Motivation / Use-Case

add e2e test for WEBPACK_SERVE env variable

Breaking Changes

None

Additional Info

No

[codecov]

Codecov Report

Merging #4125 (3a7dc0a) into master (c9b959f) will increase coverage by 0.13%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4125      +/-   ##
==========================================
+ Coverage   92.54%   92.68%   +0.13%     
==========================================
  Files          14       14              
  Lines        1462     1462              
  Branches      552      552              
==========================================
+ Hits         1353     1355       +2     
+ Misses        101       99       -2     
  Partials        8        8              

Impacted Files	Coverage Δ
lib/servers/WebsocketServer.js	97.14% <0.00%> (+5.71%)	⬆️

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