resolves #183

[jmbarbone]

• creates a temporary directory without changing random seed
• adds testing

[codecov-commenter]

Codecov Report

Merging #224 (6abdeeb) into master (57333c1) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #224      +/-   ##
==========================================
- Coverage   65.44%   65.44%   -0.01%     
==========================================
  Files          34       34              
  Lines        8879     8878       -1     
==========================================
- Hits         5811     5810       -1     
  Misses       3068     3068              

Impacted Files	Coverage Δ
R/readWorkbook.R	87.63% <100.00%> (-0.05%)	⬇️

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