fix gen_test.go

[ubogdan]

Describe the PR

• fix a typo.
• remove impossible condition

[codecov]

Codecov Report

Merging #960 (80e23bd) into master (6be354d) will increase coverage by 0.03%.
The diff coverage is 87.50%.

@@            Coverage Diff             @@
##           master     #960      +/-   ##
==========================================
+ Coverage   85.95%   85.99%   +0.03%     
==========================================
  Files           8        8              
  Lines        1823     1828       +5     
==========================================
+ Hits         1567     1572       +5     
  Misses        150      150              
  Partials      106      106              

Impacted Files	Coverage Δ
parser.go	83.29% <81.81%> (+0.05%)	⬆️
gen/gen.go	95.52% <100.00%> (+0.06%)	⬆️

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