Add SavePresetCommand testcases

[MorningLit]

No description provided.

[codecov-io]

Codecov Report

Merging #212 into master will increase coverage by 1.34%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #212      +/-   ##
============================================
+ Coverage     62.53%   63.88%   +1.34%     
- Complexity      692      705      +13     
============================================
  Files           118      118              
  Lines          2453     2453              
  Branches        283      283              
============================================
+ Hits           1534     1567      +33     
+ Misses          813      780      -33     
  Partials        106      106              

Impacted Files	Coverage Δ	Complexity Δ
...va/seedu/address/logic/commands/CommandResult.java	68.18% <ø> (ø)	8.00 <0.00> (ø)
...rc/main/java/seedu/address/model/ModelManager.java	72.97% <100.00%> (+0.90%)	38.00 <1.00> (+1.00)
...ain/java/seedu/address/storage/StorageManager.java	72.50% <100.00%> (+20.00%)	14.00 <0.00> (+4.00)
...eedu/address/storage/JsonPresetManagerStorage.java	90.47% <0.00%> (+4.76%)	7.00% <0.00%> (+1.00%)
...eedu/address/logic/commands/SavePresetCommand.java	86.66% <0.00%> (+76.66%)	10.00% <0.00%> (+7.00%)

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[ernestlim8]

LGTM