test: add more negative test cases

[tdakkota]

No description provided.

[codecov]

Codecov Report

Merging #311 (49989c8) into main (5ea7b4a) will increase coverage by 0.51%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #311      +/-   ##
==========================================
+ Coverage   67.02%   67.54%   +0.51%     
==========================================
  Files         117      117              
  Lines        7884     7887       +3     
==========================================
+ Hits         5284     5327      +43     
+ Misses       2250     2222      -28     
+ Partials      350      338      -12     

Impacted Files	Coverage Δ
openapi/parser/parse_parameter.go	94.82% <100.00%> (+13.41%)	⬆️
openapi/parser/parse_request_body.go	88.46% <100.00%> (ø)
openapi/parser/parse_response.go	85.71% <100.00%> (ø)
openapi/parser/parse_security.go	84.74% <100.00%> (+10.16%)	⬆️
openapi/parser/parser.go	81.14% <100.00%> (ø)
gen/gen_contents.go	79.31% <0.00%> (-3.45%)	⬇️
gen/schema_gen.go	79.70% <0.00%> (+1.48%)	⬆️
jsonschema/parser.go	81.84% <0.00%> (+1.91%)	⬆️
openapi/parser/parse_components.go	100.00% <0.00%> (+8.10%)	⬆️
... and 4 more

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