Add more unit tests

[seratch]

Summary

This pull request adds a few tests to the project.

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

Merging #1401 (41b4902) into main (953e77d) will increase coverage by 1.59%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1401      +/-   ##
==========================================
+ Coverage   76.97%   78.56%   +1.59%     
==========================================
  Files          17       17              
  Lines        1446     1446              
  Branches      426      426              
==========================================
+ Hits         1113     1136      +23     
+ Misses        232      211      -21     
+ Partials      101       99       -2     

Impacted Files	Coverage Δ
src/App.ts	83.64% <0.00%> (+0.94%)	⬆️
src/receivers/AwsLambdaReceiver.ts	71.59% <0.00%> (+9.09%)	⬆️
src/receivers/HTTPResponseAck.ts	48.27% <0.00%> (+37.93%)	⬆️

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