[frontend] Add tests to Environment.exportData (#1489)

[antoinemzs]

Proposed changes

• Adding unit tests to Environment.exportData

Related issues

• Contributes to [ Unit testing - simulation scope ] - import/export of a simulation (JSON) #1489

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality
• For bug fix -> I implemented a test that covers the bug

Further comments

This is just focused on the actual function that flattens objects in a collection into Excel-able structures (i.e. flat objects). This function only special-cases a few specific keys in a candidate object though.
This is part of the XLS aspect of the linked issue.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 33.73%. Comparing base (13d6e1b) to head (1e53864).
Report is 7 commits behind head on release/current.

Additional details and impacted files

@@                Coverage Diff                 @@
##             release/current    #2210   +/-   ##
==================================================
  Coverage              33.73%   33.73%           
  Complexity              1566     1566           
==================================================
  Files                    583      583           
  Lines                  18000    18000           
  Branches                1168     1168           
==================================================
  Hits                    6072     6072           
  Misses                 11635    11635           
  Partials                 293      293           

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