Expect "Create reference output" warning in tests

[pwep]

• wrapper around expect_known_output for each first use of a tempfile
• Discussed in issue #10

[codecov[bot]]

Codecov Report

Merging #12 into development will decrease coverage by 1.34%. The diff coverage is n/a.

@@               Coverage Diff               @@
##           development      #12      +/-   ##
===============================================
- Coverage         79.4%   78.06%   -1.35%     
===============================================
  Files               56       56              
  Lines             7309     7309              
===============================================
- Hits              5804     5706      -98     
- Misses            1505     1603      +98

Impacted Files	Coverage Δ
R/Compare3ProperRocFits.R	0% <0%> (-37.58%)	:arrow_down:
R/FitCbmRoc.R	62.31% <0%> (-14.01%)	:arrow_down:
R/ChisqrGoodnessOfFit.R	89.36% <0%> (-9.58%)	:arrow_down:
R/FitRsmRoc.R	84.71% <0%> (-0.64%)	:arrow_down:

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