Add more testing

[luo-git]

Updates some test cases

[codecov-io]

Codecov Report

Merging #189 into master will increase coverage by 0.93%.
The diff coverage is 34.61%.

@@             Coverage Diff              @@
##             master     #189      +/-   ##
============================================
+ Coverage     63.81%   64.75%   +0.93%     
- Complexity      505      520      +15     
============================================
  Files            97       97              
  Lines          1686     1705      +19     
  Branches        161      168       +7     
============================================
+ Hits           1076     1104      +28     
+ Misses          551      533      -18     
- Partials         59       68       +9     

Impacted Files	Coverage Δ	Complexity Δ
.../java/seedu/address/logic/commands/TagCommand.java	93.10% <ø> (ø)	11.00 <0.00> (ø)
...in/java/seedu/address/model/explorer/FileList.java	52.94% <11.11%> (-47.06%)	4.00 <1.00> (+1.00)	⬇️
...java/seedu/address/model/explorer/CurrentPath.java	74.07% <12.50%> (+5.65%)	7.00 <1.00> (+3.00)
...main/java/seedu/address/model/tag/FileAddress.java	61.53% <60.00%> (-8.47%)	7.00 <4.00> (+3.00)	⬇️
...ava/seedu/address/logic/commands/LabelCommand.java	100.00% <100.00%> (+12.50%)	10.00 <0.00> (+2.00)
...java/seedu/address/logic/commands/OpenCommand.java	52.94% <100.00%> (-2.62%)	7.00 <1.00> (-1.00)
...ava/seedu/address/logic/commands/RetagCommand.java	100.00% <100.00%> (+12.00%)	11.00 <0.00> (+2.00)
...java/seedu/address/logic/commands/ListCommand.java	100.00% <0.00%> (+20.00%)	5.00% <0.00%> (+2.00%)
... and 2 more

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[Ma-Yueran]

Thanks for the huge amount of effort, the tests looks great, LGTM!