[v1.3.2] Add Parser Test Cases

[Jargonx]

Closes #159

[codecov-io]

Codecov Report

Merging #160 into master will increase coverage by 3.25%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #160      +/-   ##
============================================
+ Coverage     65.18%   68.44%   +3.25%     
- Complexity      664      697      +33     
============================================
  Files           122      122              
  Lines          2424     2424              
  Branches        340      340              
============================================
+ Hits           1580     1659      +79     
+ Misses          711      614      -97     
- Partials        133      151      +18     

Impacted Files	Coverage Δ	Complexity Δ
...java/seedu/pivot/logic/commands/DeleteCommand.java	100.00% <ø> (ø)	1.00 <0.00> (ø)
.../seedu/pivot/logic/parser/DeleteCommandParser.java	80.00% <ø> (+53.33%)	12.00 <0.00> (+8.00)
...edu/pivot/model/investigationcase/Description.java	100.00% <ø> (ø)	6.00 <0.00> (ø)
...n/java/seedu/pivot/logic/commands/OpenCommand.java	60.00% <0.00%> (ø)	2.00% <0.00%> (+1.00%)
...main/java/seedu/pivot/logic/parser/ParserUtil.java	82.53% <0.00%> (+9.52%)	19.00% <0.00%> (+2.00%)
...ava/seedu/pivot/logic/parser/AddCommandParser.java	53.57% <0.00%> (+28.57%)	9.00% <0.00%> (+5.00%)
...va/seedu/pivot/logic/parser/OpenCommandParser.java	53.84% <0.00%> (+53.84%)	3.00% <0.00%> (+3.00%)
...u/pivot/logic/parser/AddDocumentCommandParser.java	57.14% <0.00%> (+57.14%)	3.00% <0.00%> (+3.00%)
...ivot/logic/parser/AddDescriptionCommandParser.java	72.72% <0.00%> (+72.72%)	3.00% <0.00%> (+3.00%)
... and 2 more

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[constancensq]

LGTM