Increase Test Coverage

[jeffreyad]

We should improve test coverage across the package, with priority on the files with the lowest coverage. This will help catch bugs earlier and make the codebase more maintainable.
Files needing attention

R/sort.R (51.52%) - Highest priority
R/supp.R (70.05%)
R/utils.R (75.00%)
R/labels.R (77.78%)
R/checks.R (85.44%)
R/build.R (86.84%)

[jeffreyad]

Added tests for sort and supp. Will break into sub issues