Add PureComponent related tests. #944

[theKashey]

Making it as complex, and as close to @elisherer 's example in #994, as I could.

It still works out of the box :(

[codecov-io]

Codecov Report

Merging #946 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #946   +/-   ##
=======================================
  Coverage   88.11%   88.11%           
=======================================
  Files          30       30           
  Lines         673      673           
  Branches      155      155           
=======================================
  Hits          593      593           
  Misses         65       65           
  Partials       15       15

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