Add unit-test for file merging

[HealthyPear]

No description provided.

[codecov]

Codecov Report

Merging #51 (c19aaec) into master (ebd5eef) will increase coverage by 11.48%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           master      #51       +/-   ##
===========================================
+ Coverage   10.33%   21.82%   +11.48%     
===========================================
  Files           9       10        +1     
  Lines         706      747       +41     
===========================================
+ Hits           73      163       +90     
+ Misses        633      584       -49     

Impacted Files	Coverage Δ
tests/test_merge.py	100.00% <100.00%> (ø)
merge_tables.py	71.01% <0.00%> (+71.01%)	⬆️

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