Issue 111 review unittests

[JDTheRipperPC]

Resolves #111

Removed use of an external file in unittests.

Added a new tests/utils.py to handle with the DataNavigator creation.

[CLAassistant]

All committers have signed the CLA.

[codecov-io]

Codecov Report

Merging #113 into master will increase coverage by 0.3%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master     #113     +/-   ##
=========================================
+ Coverage   72.75%   73.06%   +0.3%     
=========================================
  Files           8        8             
  Lines         646      646             
=========================================
+ Hits          470      472      +2     
+ Misses        176      174      -2

Impacted Files	Coverage Δ
sdv/data_navigator.py	100% <0%> (+2.4%)	⬆️

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