Use mock to avoid pre-checks for device add methods

This will allow coverage in some unusual error paths.

Signed-off-by: mulhern <amulhern@redhat.com>

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

@@ -15,13 +15,17 @@
 Test 'add'.
 """
 
+# isort: STDLIB
+from unittest.mock import patch
+
 # isort: FIRSTPARTY
 from dbus_client_gen import DbusClientUniqueResultError
 
 # isort: LOCAL
 from stratis_cli import StratisCliErrorCodes
 from stratis_cli._errors import (
     StratisCliEngineError,
+    StratisCliIncoherenceError,
     StratisCliInUseOtherTierError,
     StratisCliInUseSameTierError,
     StratisCliPartialChangeError,
@@ -114,6 +118,26 @@ def test_add_data_again(self):
         command_line = self._MENU + [self._POOLNAME] + self._DEVICES
         self.check_error(StratisCliPartialChangeError, command_line, _ERROR)
 
+    def test_add_data_again_mock_check(self):
+        """
+        Test that trying to add the same devices twice results in a
+        StratisCliIncoherenceError exception.
+        There are 0 target resources that would change.
+        There is 1 target resource that would not change.
+        """
+        command_line = self._MENU + [self._POOLNAME] + self._DEVICES
+        # isort: LOCAL
+        import stratis_cli  # pylint: disable=import-outside-toplevel
+
+        with patch.object(
+            # pylint: disable=protected-access
+            stratis_cli._actions._pool,  # pyright: ignore
+            "_check_same_tier",
+            autospec=True,
+            return_value=None,
+        ):
+            self.check_error(StratisCliIncoherenceError, command_line, _ERROR)
+
     def test_add_data_cache(self):
         """
         Test that adding 1 data device that is already in the cache tier raises