unit tests: sending mail with invalid recipients

tests/test_mails.py

@@ -1,3 +1,4 @@
+import smtplib
 import warnings
 from unittest import mock
 
@@ -17,6 +18,21 @@ def test_send_test_email(testclient, logged_admin, smtpd):
     assert len(smtpd.messages) == 1
 
 
+@mock.patch("smtplib.SMTP")
+def test_send_test_email_recipient_refused(SMTP, testclient, logged_admin, smtpd):
+    SMTP.side_effect = mock.Mock(
+        side_effect=smtplib.SMTPRecipientsRefused("test@test.com")
+    )
+    assert len(smtpd.messages) == 0
+
+    res = testclient.get("/admin/mail")
+    res.form["mail"] = "test@test.com"
+    res = res.form.submit()
+    assert "The test invitation mail has been sent correctly" in res.text
+
+    assert len(smtpd.messages) == 0
+
+
 @mock.patch("smtplib.SMTP")
 def test_send_test_email_failed(SMTP, testclient, logged_admin):
     SMTP.side_effect = mock.Mock(side_effect=OSError("unit test mail error"))