Add unit tests and codecov

[joshuali925]

Description

• Add unit test
• Add codecov
• Add CI badges to readme

Issues Resolved

#18

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (main@57a4780). Click here to learn what that means.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #19   +/-   ##
=======================================
  Coverage        ?   95.30%           
=======================================
  Files           ?        5           
  Lines           ?      149           
  Branches        ?       45           
=======================================
  Hits            ?      142           
  Misses          ?        7           
  Partials        ?        0           

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