fix: check loopback before cert creation

tests/test_cert_manager.py

@@ -4,6 +4,8 @@ import subprocess
 import typing
 import unittest.mock
 
+import requests
+
 from stapler.cert_manager import CertManager, CertManagerError
 from stapler.params import Parameters
 
@@ -170,10 +172,24 @@ class TestRegistry(BaseTestCase):
                 self.socket_mock, None, self.context_mock
             )
 
-    def test_servername_callback_fail(self) -> None:
+    def test_servername_callback_fail_no_valid_host(self) -> None:
         self._make_self_signed("example.com")
+        with (
+            self.patch("requests.head") as request_mock,
+            self.patch("ssl.create_default_context", count=0),
+        ):
+            request_mock.side_effect = Exception()
+            self.cert_manager.servername_callback(
+                self.socket_mock, "example.fr", self.context_mock
+            )
+
+    def test_servername_callback_fail_no_binaries(self) -> None:
+        self._make_self_signed("example.com")
+        response = requests.Response()
+        response.status_code = 200
         with (
             self.patch("shutil.which", count=3),
+            self.patch("requests.head", response),
             self.patch("ssl.create_default_context", count=0),
         ):
             self.cert_manager.servername_callback(