Add nested testsets to CircularBuffer

[oxinabox]

Contributes towards fixing #412

[codecov]

Codecov Report

Merging #413 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #413   +/-   ##
=======================================
  Coverage   98.66%   98.66%           
=======================================
  Files          30       30           
  Lines        1719     1719           
=======================================
  Hits         1696     1696           
  Misses         23       23

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