Add tests for expense (storage, parser)

[yanlynnnnn]

Add tests for expense (storage, parser)

[codecov-io]

Codecov Report

Merging #212 into master will increase coverage by 5.35%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #212      +/-   ##
============================================
+ Coverage     45.63%   50.98%   +5.35%     
- Complexity      816      895      +79     
============================================
  Files           205      205              
  Lines          3850     3852       +2     
  Branches        442      443       +1     
============================================
+ Hits           1757     1964     +207     
+ Misses         1991     1773     -218     
- Partials        102      115      +13     

Impacted Files	Coverage Δ	Complexity Δ
...erce/logic/commands/expense/AddExpenseCommand.java	100.00% <ø> (ø)	3.00 <0.00> (ø)
...e/logic/commands/expense/DeleteExpenseCommand.java	100.00% <ø> (ø)	7.00 <0.00> (ø)
...rce/logic/commands/expense/EditExpenseCommand.java	76.47% <ø> (+4.41%)	8.00 <0.00> (ø)
...rce/logic/commands/expense/FindExpenseCommand.java	100.00% <ø> (+100.00%)	7.00 <0.00> (+7.00)
...rce/logic/commands/expense/SortExpenseCommand.java	100.00% <ø> (+100.00%)	2.00 <0.00> (+2.00)
...torage/expense/JsonSerializableExpenseTracker.java	71.05% <ø> (+60.52%)	8.00 <0.00> (+7.00)
...du/homerce/storage/expense/JsonAdaptedExpense.java	76.92% <100.00%> (+76.92%)	12.00 <2.00> (+12.00)
...main/java/seedu/homerce/model/expense/Expense.java	85.29% <0.00%> (-2.95%)	11.00% <0.00%> (-1.00%)
...va/seedu/homerce/model/manager/ExpenseTracker.java	78.94% <0.00%> (+15.78%)	13.00% <0.00%> (+4.00%)
... and 14 more

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[khoongwk]

LGTM