test: fulfill email sendEmail TODO — assert emailProvider.sendEmail is called

The existing test had a TODO comment noting that it should assert
emailProvider.sendEmail was called but only verified no exceptions were thrown.

Now uses vi.spyOn to verify:
- emailProvider.sendEmail is called exactly once
- called with the correct recipient address
- called with an html body that includes the magic link URL

email-provider.server.ts already short-circuits in test mode (returns
Promise.resolve without hitting Mailgun), so no mocking of HTTP is needed.

Author: wheeljackz

app/services/__tests__/email.server.test.ts

@@ -1,11 +1,19 @@
+import { vi, describe, it, expect, beforeEach } from 'vitest'
 import { User } from '@prisma/client'
 import { sendEmail } from '../email.server'
+import * as emailProvider from '~/services/email-provider.server'
 import { userBuilder } from '~/models/__mocks__/user'
 
 describe('sendEmail', () => {
   const user = userBuilder() as User
 
+  beforeEach(() => {
+    vi.restoreAllMocks()
+  })
+
   it('call emailProvider.sendEmail method', async () => {
+    const spy = vi.spyOn(emailProvider, 'sendEmail')
+
     await sendEmail({
       emailAddress: user.email,
       magicLink: 'http://localhost:3000/magic',
@@ -14,6 +22,14 @@ describe('sendEmail', () => {
       form: new FormData(),
     })
 
-    // TODO: assert emailProvider.sendEmail was called
+    expect(spy).toHaveBeenCalledOnce()
+    expect(spy).toHaveBeenCalledWith(
+      expect.objectContaining({
+        to: user.email,
+        from: expect.any(String),
+        subject: expect.any(String),
+        html: expect.stringContaining('localhost:3000/magic'),
+      })
+    )
   })
 })