6318 - New Supervisor System Spec Overhaul

[AudTheCodeWitch]

What github issue is this PR for, if any?

Resolves #6318

What changed, and why?

This PR refactors the system spec for creating a new supervisor (spec/system/supervisors/new_spec.rb) to make it more reliable, comprehensive, and readable.

The original tests were flaky because they checked the database (change(User, :count)) without explicitly waiting for the page to load after the form submission. They also didn't test for validation errors (the "sad path") or cover all user authorization cases.

Key changes:

• Stubbed External API: Added a stub_request for the api.short.io URL shortener. This was causing WebMock errors when a phone number was provided and is a best practice for system tests.
• Explicit Waits: Fixed flakiness in path-checking tests. We now wait for a success or error message (expect(page).to have_text(...)) before checking the have_current_path, ensuring the redirect or re-render has completed.
• DRY "Happy Path": Refactored the admin tests into a shared context "with valid form submission". This block fills in and submits the form once in a before block, making the suite faster.
• Single-Purpose Tests: Broke the "happy path" assertions into small, focused it blocks to test individual outcomes:
  • Shows a success message
  • Redirects to the correct page
  • Persists the data correctly in the database
  • Sends the invitation email
• Added "Sad Path": Added a new context "with invalid form submission" to ensure validation errors are displayed and that no user is created.
• Added Authorization Tests: Added contexts to verify that both supervisor and volunteer users are correctly redirected with an "unauthorized" message.

How is this tested? 💖💪

• Refactored spec/system/supervisors/new_spec.rb
• Ran 100 times locally with no flakes!

Screenshots please 📸

Feelings gif

[compwron]

nice!