Closes #302 Adding Snapshot testing guidance to unit testing vignette #633

Job	Run time
Documentation	0s
Render README	0s
Validation	0s
Links / Validate Links	6s
Code Coverage / Get R version	2s
Check / (4.1)	2m 15s
Check / (4.2)	2m 16s
Check / (4.3)	2m 8s
Lint / Get R version	1s
Man Pages / Get R version	1s
Spelling / Get R version	1s
Code Style / Get R version	1s
Code Style / Code Style	1m 46s
Man Pages / Roxygen	1m 45s
Lint / Lint	2m 7s
Spelling / Spellcheck	2m 6s
Code Coverage / Test Coverage	2m 5s
Code Coverage / Generate badge for coverage	1s
	16m 41s

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