Basic refactoring + unit tests

[luminousmen]

No description provided.

[codecov-commenter]

Codecov Report

Merging #14 (b7f2c3c) into master (117a97f) will increase coverage by 1.6%.
The diff coverage is 93.3%.

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@@           Coverage Diff            @@
##           master     #14     +/-   ##
========================================
+ Coverage    89.3%   91.0%   +1.6%     
========================================
  Files           7       7             
  Lines         489     467     -22     
========================================
- Hits          437     425     -12     
+ Misses         52      42     -10     

Files	Coverage Δ
src/data_toolset/main.py	94.6% <100.0%> (-3.1%)	⬇️
src/data_toolset/utils/avro.py	98.5% <100.0%> (+1.9%)	⬆️
src/data_toolset/utils/mixins.py	69.5% <ø> (+13.3%)	⬆️
src/data_toolset/utils/parquet.py	96.3% <100.0%> (+1.5%)	⬆️
src/data_toolset/utils/base.py	82.1% <75.0%> (+0.1%)	⬆️