Add more tests

[marquestye]

Added tests for Module and its fields.
Added tests to UserPrefs and ModuleData.
Removed depreciated methods in ModuleData.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (fd8946c) 74.30% compared to head (0fb0321) 76.59%.

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Additional details and impacted files

@@             Coverage Diff              @@
##             master     #233      +/-   ##
============================================
+ Coverage     74.30%   76.59%   +2.29%     
- Complexity      525      554      +29     
============================================
  Files            78       78              
  Lines          1755     1752       -3     
  Branches        178      178              
============================================
+ Hits           1304     1342      +38     
+ Misses          379      354      -25     
+ Partials         72       56      -16     

Files	Coverage Δ
src/main/java/seedu/address/model/ModuleData.java	94.44% <ø> (+9.82%)	⬆️
...n/java/seedu/address/model/module/Description.java	100.00% <ø> (+21.42%)	⬆️
...java/seedu/address/model/module/ModularCredit.java	100.00% <100.00%> (+26.66%)	⬆️
...in/java/seedu/address/model/module/ModuleName.java	100.00% <ø> (+21.42%)	⬆️

... and 7 files with indirect coverage changes

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[rocketninja7]

LGTM 👍