Add some missing UT cases

[vsoulgard]

Just some missing UT cases.

throttling_with_non_throttled_request might look little bit tricky, it should cover this line:

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.46%. Comparing base (a4ecbdb) to head (07b7c35).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #51      +/-   ##
===========================================
+ Coverage    96.24%   96.46%   +0.21%     
===========================================
  Files           44       44              
  Lines         3250     3250              
===========================================
+ Hits          3128     3135       +7     
+ Misses         122      115       -7     

see 4 files with indirect coverage changes

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[biljazovic]

Thanks, merged.
I modified throttling_ordering test to cover that case in async_sender