garbage collect test reference.

[dnozay]

see #105, #112.

[codecov-io]

Current coverage is 98.61%

Merging #129 into master will increase coverage by +0.02% as of ccecb74

@@            master    #129   diff @@
======================================
  Files           17      17       
  Stmts         1065    1083    +18
  Branches         0       0       
  Methods          0       0       
======================================
+ Hit           1050    1068    +18
  Partial          0       0       
  Missed          15      15       

Review entire Coverage Diff as of ccecb74

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