Add test for 'func (*Response) After'

[iwamot]

No description provided.

[codecov]

Codecov Report

Merging #1558 into master will increase coverage by 0.18%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1558      +/-   ##
==========================================
+ Coverage   84.94%   85.13%   +0.18%     
==========================================
  Files          28       28              
  Lines        2166     2166              
==========================================
+ Hits         1840     1844       +4     
+ Misses        211      208       -3     
+ Partials      115      114       -1     

Impacted Files	Coverage Δ
response.go	86.84% <0.00%> (+10.52%)	⬆️

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