Add tests for tag and untag command

[ernestlim8]

No description provided.

[codecov-io]

Codecov Report

Merging #218 into master will increase coverage by 2.29%.
The diff coverage is 28.57%.

@@             Coverage Diff              @@
##             master     #218      +/-   ##
============================================
+ Coverage     64.00%   66.29%   +2.29%     
- Complexity      707      728      +21     
============================================
  Files           118      118              
  Lines          2456     2451       -5     
  Branches        284      287       +3     
============================================
+ Hits           1572     1625      +53     
+ Misses          777      713      -64     
- Partials        107      113       +6     

Impacted Files	Coverage Δ	Complexity Δ
.../java/seedu/address/logic/commands/TagCommand.java	65.00% <0.00%> (-11.48%)	5.00 <1.00> (+1.00)	⬇️
...ava/seedu/address/logic/commands/UntagCommand.java	66.66% <0.00%> (-8.34%)	5.00 <1.00> (+1.00)	⬇️
src/main/java/seedu/address/model/menu/Menu.java	92.98% <ø> (+15.04%)	26.00 <0.00> (ø)
...a/seedu/address/logic/parser/TagCommandParser.java	100.00% <100.00%> (+100.00%)	4.00 <0.00> (+4.00)
...seedu/address/logic/parser/UntagCommandParser.java	100.00% <100.00%> (+100.00%)	2.00 <0.00> (+2.00)
...rc/main/java/seedu/address/model/ModelManager.java	74.77% <0.00%> (+1.80%)	39.00% <0.00%> (+1.00%)
...in/java/seedu/address/logic/parser/ParserUtil.java	92.68% <0.00%> (+3.65%)	34.00% <0.00%> (+2.00%)
...c/main/java/seedu/address/model/food/MenuItem.java	100.00% <0.00%> (+37.50%)	4.00% <0.00%> (+1.00%)
... and 1 more

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[MorningLit]

lgtm