chore: re-add unit test for pusing certs to container

Signed-off-by: guillaume <guillaume.belanger27@gmail.com>

tests/unit/test_charm.py

@@ -28,6 +28,12 @@
 
 
 class TestCharm:
+    @pytest.fixture(autouse=True)
+    def setup(self):
+        self.mock_open = mock_open()
+        self.patcher = patch("builtins.open", self.mock_open)
+        self.patcher.start()
+
     @pytest.fixture(autouse=True)
     def context(self):
         self.ctx = scenario.Context(
@@ -85,6 +91,30 @@ def test_given_valid_config_when_collect_unit_status_then_status_is_active(
 
         assert state_out.unit_status == ActiveStatus()
 
+    @patch("charm.generate_private_key")
+    @patch("charm.generate_ca")
+    def test_given_valid_config_when_config_changed_then_ca_certificate_is_pushed_to_charm_container(  # noqa: E501
+        self,
+        patch_generate_ca,
+        patch_generate_private_key,
+    ):
+        ca_certificate_string = "whatever CA certificate"
+        private_key_string = "whatever private key"
+        patch_generate_ca.return_value = ca_certificate_string
+        patch_generate_private_key.return_value = private_key_string
+        state_in = scenario.State(
+            config={
+                "ca-common-name": "pizza.com",
+                "certificate-validity": 100,
+                "root-ca-validity": 200,
+            },
+            leader=True,
+        )
+
+        self.ctx.run(event="config_changed", state=state_in)
+
+        self.mock_open.return_value.write.assert_called_with(ca_certificate_string)
+
     @patch("charm.generate_private_key")
     @patch("charm.generate_ca")
     def test_given_valid_config_when_config_changed_then_ca_certificate_is_stored_in_juju_secret(