Add update stock descriptor test

[AudreyFelicio]

No description provided.

[codecov-io]

Codecov Report

Merging #313 (5dd6417) into master (bb23e02) will increase coverage by 0.422%.
The diff coverage is 100.000%.

@@               Coverage Diff               @@
##              master      #313       +/-   ##
===============================================
+ Coverage     72.076%   72.499%   +0.422%     
- Complexity      1010      1033       +23     
===============================================
  Files            128       128               
  Lines           3481      3509       +28     
  Branches         474       484       +10     
===============================================
+ Hits            2509      2544       +35     
+ Misses           801       796        -5     
+ Partials         171       169        -2     

Impacted Files	Coverage Δ	Complexity Δ
...java/seedu/stock/logic/commands/UpdateCommand.java	89.915% <100.000%> (+7.009%)	18.000 <0.000> (ø)
...rc/main/java/seedu/stock/model/stock/Quantity.java	96.428% <0.000%> (+3.571%)	13.000% <0.000%> (+1.000%)
...java/seedu/stock/logic/commands/CommandResult.java	56.363% <0.000%> (+4.639%)	22.000% <0.000%> (+18.000%)
...rc/main/java/seedu/stock/model/stock/Location.java	90.000% <0.000%> (+10.000%)	6.000% <0.000%> (+1.000%)
src/main/java/seedu/stock/logic/parser/Prefix.java	91.666% <0.000%> (+16.666%)	7.000% <0.000%> (+1.000%)
...in/java/seedu/stock/logic/commands/TabCommand.java	100.000% <0.000%> (+50.000%)	4.000% <0.000%> (+1.000%)
...n/java/seedu/stock/logic/commands/ExitCommand.java	100.000% <0.000%> (+50.000%)	3.000% <0.000%> (+1.000%)

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[Ashley-Lau]

LGTM!