Closes #106: improve test coverage #340

Job	Run time
Get R version	3s
Check / macos-latest (release)	21s
Check / windows-latest (release)	23s
Check / ubuntu-latest (release)	20s
Links / Validate Links	5s
Version Bump	0s
Code Coverage / Test Coverage	14s
Lint / Lint	15s
Spelling / Spellcheck	14s
Man Pages / Roxygen	14s
Check Templates / Verify	14s
Code Style / Code Style	15s
Documentation	0s
Validation	-1s
Code Coverage / Generate badge for coverage	1s
	2m 38s

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