♻️(backend) refacto email invitation

Remove email invitation from Invitation model
to be able to use it in other context.
We add it in utils.py instead, and it will be called
from the viewset.
We add the document_id to link to the document from
the mail.

src/backend/core/tests/test_utils.py

@@ -0,0 +1,86 @@
+"""
+Unit tests for the Invitation model
+"""
+import smtplib
+from logging import Logger
+from unittest import mock
+
+from django.core import mail
+
+import pytest
+
+from core.utils import email_invitation
+
+pytestmark = pytest.mark.django_db
+
+
+def test_utils__email_invitation_success():
+    """
+    The email invitation is sent successfully.
+    """
+    # pylint: disable-next=no-member
+    assert len(mail.outbox) == 0
+
+    email_invitation("en", "guest@example.com", "123-456-789")
+
+    # pylint: disable-next=no-member
+    assert len(mail.outbox) == 1
+
+    # pylint: disable-next=no-member
+    email = mail.outbox[0]
+
+    assert email.to == ["guest@example.com"]
+    email_content = " ".join(email.body.split())
+    assert "Invitation to join Docs!" in email_content
+    assert "docs/123-456-789/" in email_content
+
+
+def test_utils__email_invitation_success_fr():
+    """
+    The email invitation is sent successfully in french.
+    """
+    # pylint: disable-next=no-member
+    assert len(mail.outbox) == 0
+
+    email_invitation("fr-fr", "guest@example.com", "123-456-789")
+
+    # pylint: disable-next=no-member
+    assert len(mail.outbox) == 1
+
+    # pylint: disable-next=no-member
+    email = mail.outbox[0]
+
+    assert email.to == ["guest@example.com"]
+    email_content = " ".join(email.body.split())
+    assert "Invitation à rejoindre Docs !" in email_content
+    assert "docs/123-456-789/" in email_content
+
+
+@mock.patch(
+    "core.utils.send_mail",
+    side_effect=smtplib.SMTPException("Error SMTPException"),
+)
+@mock.patch.object(Logger, "error")
+def test_utils__email_invitation_failed(mock_logger, _mock_send_mail):
+    """Check mail behavior when an SMTP error occurs when sent an email invitation."""
+
+    # pylint: disable-next=no-member
+    assert len(mail.outbox) == 0
+
+    email_invitation("en", "guest@example.com", "123-456-789")
+
+    # No email has been sent
+    # pylint: disable-next=no-member
+    assert len(mail.outbox) == 0
+
+    # Logger should be called
+    mock_logger.assert_called_once()
+
+    (
+        _,
+        email,
+        exception,
+    ) = mock_logger.call_args.args
+
+    assert email == "guest@example.com"
+    assert isinstance(exception, smtplib.SMTPException)