add tests for interfaces view

[codeEmpress1]

Done

• Add tests for interfaces view

How to QA

Issue / Card

Fixes #

Screenshots

[webteam-app]

Demo starting at https://charmhub-io-1768.demos.haus

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 57.10%. Comparing base (a81444a) to head (b9845f9).
Report is 34 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1768      +/-   ##
==========================================
+ Coverage   53.87%   57.10%   +3.23%     
==========================================
  Files          30       32       +2     
  Lines        2246     2280      +34     
==========================================
+ Hits         1210     1302      +92     
+ Misses       1036      978      -58     

Files with missing lines	Coverage Δ
tests/interfaces/test_single_interface.py	100.00% <100.00%> (ø)

... and 4 files with indirect coverage changes

[abbiesims]

LGTM! 👍