test: Add tests for typing indicator

[atomrc]

Description

Add tests that cover the scenario fixed by #15985

Checklist

• PR has been self reviewed by the author;
• Hard-to-understand areas of the code have been commented;
• If it is a core feature, unit tests have been added;

[codecov]

Codecov Report

Merging #15986 (1bae169) into dev (3f8fbd1) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev   #15986   +/-   ##
=======================================
  Coverage   44.60%   44.61%           
=======================================
  Files         686      686           
  Lines       22909    22909           
  Branches     5201     5201           
=======================================
+ Hits        10219    10220    +1     
  Misses      11376    11376           
+ Partials     1314     1313    -1