Add test for AddCommand

[aidoxe-123]

Improve test coverage

[codecov-io]

Codecov Report

Merging #70 into master will increase coverage by 0.21%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master      #70      +/-   ##
============================================
+ Coverage     72.58%   72.80%   +0.21%     
- Complexity      415      416       +1     
============================================
  Files            73       73              
  Lines          1375     1375              
  Branches        107      107              
============================================
+ Hits            998     1001       +3     
+ Misses          337      335       -2     
+ Partials         40       39       -1     

Impacted Files	Coverage Δ	Complexity Δ
.../java/jimmy/mcgymmy/logic/commands/AddCommand.java	100.00% <0.00%> (+13.04%)	4.00% <0.00%> (+1.00%)

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[Jh123x]

LGTM ! Just need to resolve the conflict

[Jh123x]

LGTM!