update benchmark documentation to match code

[Brijeshthummar02]

issue #444

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.48%. Comparing base (72f40f9) to head (6447dfb).
Report is 6 commits behind head on latest.

Additional details and impacted files

@@           Coverage Diff           @@
##           latest     #452   +/-   ##
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  Coverage   90.48%   90.48%           
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  Files          47       47           
  Lines        4373     4373           
  Branches      585      585           
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  Hits         3957     3957           
  Misses        281      281           
  Partials      135      135           

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[goatshriek]

Please review the actual test in test/function/element.cpp, this change does not completely bring the two into matching.

Thank you for refactoring with the fixture function! Be sure that you update the actual test as well as the docs with the refactored code, to ensure that it compiles and works correctly.