Generate warning when a goodValue file is missing

[pwep]

• the test will create the file using saveRDS
• our intention is to distribute goodValue files
• missing file warning(s) indicates an incomplete distribution
• no warning means test will compare new object against goodValue

[codecov[bot]]

Codecov Report

Merging #20 into development will not change coverage. The diff coverage is n/a.

@@             Coverage Diff              @@
##           development      #20   +/-   ##
============================================
  Coverage        64.61%   64.61%           
============================================
  Files               56       56           
  Lines             7314     7314           
============================================
  Hits              4726     4726           
  Misses            2588     2588

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