refactor: improve coverage

[kanru]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 69.87952% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.19%. Comparing base (1af1ef2) to head (a7e800b).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
src/ibus-chewing-engine.c	58.69%	19 Missing ⚠️
src/main.c	0.00%	5 Missing ⚠️
src/ibus-chewing-preedit.c	96.42%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #280      +/-   ##
==========================================
+ Coverage   69.83%   71.19%   +1.36%     
==========================================
  Files          15       15              
  Lines        2002     1951      -51     
  Branches      258      255       -3     
==========================================
- Hits         1398     1389       -9     
+ Misses        599      557      -42     
  Partials        5        5              

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