Add failing test for isMemo bug (#2390)

[bdwain]

This is in response to #2390 . By throwing away the type information of the render result, we cause isMemo checks to fail on elements that have gone through the wrapper. Ideally they would pass the isMemo check

[codecov]

Codecov Report

Merging #2408 (42d5f9e) into master (f046079) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2408   +/-   ##
=======================================
  Coverage   96.31%   96.31%           
=======================================
  Files          49       49           
  Lines        4204     4207    +3     
  Branches     1130     1130           
=======================================
+ Hits         4049     4052    +3     
  Misses        155      155           

Impacted Files	Coverage Δ
...e-adapter-react-16.1/src/ReactSixteenOneAdapter.js	95.03% <0.00%> (-0.02%)	⬇️
...e-adapter-react-16.2/src/ReactSixteenTwoAdapter.js	95.09% <0.00%> (-0.02%)	⬇️
...adapter-react-16.3/src/ReactSixteenThreeAdapter.js	95.45% <0.00%> (-0.02%)	⬇️
...enzyme-adapter-react-16/src/ReactSixteenAdapter.js	95.46% <0.00%> (ø)
packages/enzyme/src/ShallowWrapper.js	99.12% <0.00%> (+<0.01%)	⬆️
packages/enzyme/src/selectors.js	96.46% <0.00%> (+0.01%)	⬆️
...nzyme-adapter-react-13/src/ReactThirteenAdapter.js	94.96% <0.00%> (+0.03%)	⬆️

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