add testplan tests to improve code coverage

[polatengin]

Improve Core code coverage from;

----------------|---------|----------|---------|---------|------------------------------------------------------
File            | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s                                    
----------------|---------|----------|---------|---------|------------------------------------------------------
   testplan.ts  |   40.57 |     7.69 |   45.45 |    40.9 | 95-103,124-175,230-269
----------------|---------|----------|---------|---------|------------------------------------------------------

to

----------------|---------|----------|---------|---------|------------------------------------------------------
File            | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s                                    
----------------|---------|----------|---------|---------|------------------------------------------------------
   testplan.ts  |   98.55 |    84.61 |     100 |   98.48 | 269
----------------|---------|----------|---------|---------|------------------------------------------------------

GitHub issue number

#57 (Don't close the issue, there are other tools to improve test coverages)

Associated Risks

None

✅ PR Checklist

• I have read the contribution guidelines
• I have read the code of conduct guidelines
• Title of the pull request is clear and informative.
• 👌 Code hygiene
• 🔭 Telemetry added, updated, or N/A
• 📄 Documentation added, updated, or N/A
• 🛡️ Automated tests added, or N/A

🧪 How did you test it?

Run npm run test in the project root

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (main@7e53fb4). Learn more about missing BASE report.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #266   +/-   ##
=======================================
  Coverage        ?   86.29%           
=======================================
  Files           ?       10           
  Lines           ?      467           
  Branches        ?       56           
=======================================
  Hits            ?      403           
  Misses          ?       60           
  Partials        ?        4           

Flag	Coverage Δ
unittests	86.29% <ø> (?)

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