Increase code coverage

[smyrick]

Add more unit tests and remove duplicate default values to increase code coverage

[codecov-io]

Codecov Report

Merging #331 into master will increase coverage by 0.7%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##             master     #331     +/-   ##
===========================================
+ Coverage     96.11%   96.82%   +0.7%     
- Complexity      274      278      +4     
===========================================
  Files            80       81      +1     
  Lines           979      976      -3     
  Branches        180      180             
===========================================
+ Hits            941      945      +4     
+ Misses           11        6      -5     
+ Partials         27       25      -2

Impacted Files	Coverage Δ	Complexity Δ
...hql/directives/KotlinSchemaDirectiveEnvironment.kt	93.33% <ø> (+24.91%)	13 <0> (+2)	⬆️
...iagroup/graphql/generator/types/FunctionBuilder.kt	100% <ø> (ø)	7 <0> (-1)	⬇️
.../expediagroup/graphql/generator/SchemaGenerator.kt	100% <ø> (+2.27%)	23 <0> (ø)	⬇️
...ediagroup/graphql/generator/types/ScalarBuilder.kt	100% <ø> (+4%)	7 <0> (ø)	⬇️
...phql/directives/KotlinFieldDirectiveEnvironment.kt	100% <100%> (ø)	3 <3> (?)

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