Add field descriptor test

[NgChunMan]

No description provided.

[netlify]

✅ Deploy Preview for tp-preview ready!

Name	Link
🔨 Latest commit	68e259a
🔍 Latest deploy log	https://app.netlify.com/sites/tp-preview/deploys/654075b33a0b9600093911fc
😎 Deploy Preview	https://deploy-preview-182--tp-preview.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[codecov]

Codecov Report

Merging #182 (68e259a) into master (b4aed85) will increase coverage by 0.79%.
Report is 1 commits behind head on master.
The diff coverage is 16.66%.

@@             Coverage Diff              @@
##             master     #182      +/-   ##
============================================
+ Coverage     54.26%   55.05%   +0.79%     
- Complexity      592      606      +14     
============================================
  Files           119      119              
  Lines          2779     2779              
  Branches        336      336              
============================================
+ Hits           1508     1530      +22     
+ Misses         1075     1049      -26     
- Partials        196      200       +4     

Files	Coverage Δ
src/main/java/seedu/address/MainApp.java	0.00% <0.00%> (ø)
...edu/address/model/field/EditStudentDescriptor.java	85.36% <20.00%> (+41.46%)	⬆️

... and 1 file with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[NereusWB922]

LGTM