Use mock to avoid pre-checks for device add methods

This will allow coverage in some unusual error paths.

Signed-off-by: mulhern <[email protected]>

Author: mulkieran

src/stratis_cli/_actions/_pool.py

@@ -550,7 +550,7 @@ def add_data_devices(namespace: Namespace):  # pylint: disable=too-many-locals
         if return_code != StratisdErrors.OK:  # pragma: no cover
             raise StratisCliEngineError(return_code, message)
 
-        if not added or len(devs_added) < len(blockdevs):  # pragma: no cover
+        if not added or len(devs_added) < len(blockdevs):
             devnodes_added = [
                 MODev(info).Devnode()
                 for (object_path, info) in devs(

tests/integration/pool/test_add.py

@@ -15,6 +15,9 @@
 Test 'add'.
 """
 
+# isort: STDLIB
+from unittest.mock import create_autospec
+
 # isort: FIRSTPARTY
 from dbus_client_gen import DbusClientUniqueResultError
 
@@ -173,6 +176,14 @@ def test_add_data(self):
         command_line = self._MENU + [self._POOLNAME] + self._SECOND_DEVICES
         self.check_error(StratisCliInUseSameTierError, command_line, _ERROR)
 
+    def test_add_data_mock_check(self):
+        """
+        Test that adding the same devices to the data tier in a different pool fails.
+        """
+        command_line = self._MENU + [self._POOLNAME] + self._SECOND_DEVICES
+        with create_autospec("_actions._pool._check_opposite_tier", return_value=None):
+            self.check_error(StratisCliEngineError, command_line, _ERROR)
+
 
 class AddCacheTestCase1(SimTestCase):
     """