diff --git a/tests/test_linux.py b/tests/test_linux.py
index 41c8ed1..6972396 100644
--- a/tests/test_linux.py
+++ b/tests/test_linux.py
@@ -22,6 +22,11 @@ def driver():
     d._secret = "pass"  # noqa: S105
     d._forced_pkg_manager = None
     d._pkg_manager = "apt"
+    # Set by __init__, which this fixture bypasses via __new__. Without it every
+    # call through _sudo() raises AttributeError, which the callers' broad
+    # `except Exception` turns into a plain {"success": False} -- so the tests
+    # failed for a reason that had nothing to do with what they were testing.
+    d._sudo_password = None
     d.netmiko_optional_args = {}
     d._device = MagicMock()
     return d
@@ -179,7 +184,7 @@ APT_UPGRADABLE = (
 
 def test_get_available_updates_apt(driver):
     driver._pkg_manager = "apt"
-    with patch.object(driver, "_send", side_effect=["", APT_UPGRADABLE]):
+    with patch.object(driver, "_send", return_value=APT_UPGRADABLE):
         updates = driver.get_available_updates()
     assert len(updates) == 2
     assert updates[0]["name"] == "openssh-server"
@@ -312,7 +317,10 @@ def test_apply_updates_apt_all_packages(driver):
     driver._pkg_manager = "apt"
     sent_commands = []
 
-    def capture_send(cmd):
+    def capture_send(cmd, **kwargs):
+        # _sudo() passes read_timeout as a keyword; without **kwargs this raises
+        # TypeError, which the caller's `except Exception` reports as a failed
+        # upgrade rather than a broken test double.
         sent_commands.append(cmd)
         return APT_UPGRADE_SUCCESS