Add tests for top level structs and enums

[fvictorio]

Closes #243

[codecov]

Codecov Report

Merging #263 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #263   +/-   ##
=======================================
  Coverage   99.69%   99.69%           
=======================================
  Files          85       85           
  Lines         666      666           
  Branches      124      124           
=======================================
  Hits          664      664           
  Misses          2        2           

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