Add test for minimum_redundancy with REDUNDANCY policy

Adds a test which verifies how minimum_redundancy interacts with the
REDUNDANCY retention policy.

This does not really make sense as a command which a user would run
however it is still a valid retention policy and Barman will apply
it.

tests/test_barman_cloud_backup_delete.py

@@ -472,6 +472,72 @@ def test_delete_by_recovery_window_policy_with_redundancy(
             get_cloud_interface_mock, backup_metadata, expected_deleted_backups
         )
 
+    @pytest.mark.parametrize(
+        ("minimum_redundancy", "num_backups_deleted"),
+        (
+            # With a minimum_redundancy of zero, three of the four backups should be
+            # deleted (the newest is retained due to REDUNDANCY 1).
+            (0, 3),
+            # With a minimum_redundancy of one, three of the four backups should be
+            # deleted.
+            (1, 3),
+            # With a minimum_redundancy of two, two of the four backups should be
+            # deleted.
+            (2, 2),
+            # With a minimum_redundancy of three, one of the four backups should be
+            # deleted.
+            (3, 1),
+            # With a minimum_redundancy of four, none of the four backups should be
+            # deleted.
+            (4, 0),
+        ),
+    )
+    @mock.patch("barman.retention_policies.datetime")
+    @mock.patch("barman.clients.cloud_backup_delete.CloudBackupCatalog")
+    @mock.patch("barman.clients.cloud_backup_delete.get_cloud_interface")
+    def test_delete_by_redundancy_policy_with_minimum_redundancy(
+        self,
+        get_cloud_interface_mock,
+        cloud_backup_catalog_mock,
+        datetime_mock,
+        minimum_redundancy,
+        num_backups_deleted,
+    ):
+        """
+        Test that the minimum redundancy value is applied to recovery window
+        retention policy
+        """
+        # GIVEN a backup catalog with four daily backups and no WALs
+        out_of_policy_backup_ids = [
+            "20210723T095432",  # Eligible for deletion
+            "20210724T095432",  # Eligible for deletion
+            "20210725T095432",  # Eligible for deletion
+            "20210726T095432",  # Required by REDUNDANCY 1
+        ]
+        backup_metadata = self._create_backup_metadata(out_of_policy_backup_ids)
+
+        # AND a CloudBackupCatalog which returns the backup_info for only those backups
+        cloud_backup_catalog_mock.return_value = self._create_catalog(backup_metadata)
+
+        # WHEN barman-cloud-backup-delete runs, specifying a retention policy of
+        # `REDUNDANCY 1` and a given minimum_redundancy.
+        cloud_backup_delete.main(
+            [
+                "cloud_storage_url",
+                "test_server",
+                "--retention-policy",
+                "REDUNDANCY 1",
+                "--minimum-redundancy",
+                str(minimum_redundancy),
+            ]
+        )
+
+        # THEN only the expected backups are deleted
+        expected_deleted_backups = out_of_policy_backup_ids[:num_backups_deleted]
+        self._verify_only_these_backups_deleted(
+            get_cloud_interface_mock, backup_metadata, expected_deleted_backups
+        )
+
     @mock.patch("barman.clients.cloud_backup_delete.CloudBackupCatalog")
     @mock.patch(
         "barman.clients.cloud_backup_delete.get_snapshot_interface_from_backup_info"