Test activate without detach

Signed-off-by: Piotr Debski <piotr.debski@intel.com>

test/functional/api/cas/cli_messages.py

@@ -1,5 +1,5 @@
 #
-# Copyright(c) 2019-2021 Intel Corporation
+# Copyright(c) 2019-2022 Intel Corporation
 # SPDX-License-Identifier: BSD-3-Clause
 #
 import re
@@ -161,6 +161,10 @@ error_activating_cache = [
     r"Error activating cache \d+"
 ]
 
+activate_without_detach = [
+    r"Cannot open the device exclusively. Make sure to detach cache before activation."
+]
+
 
 def check_stderr_msg(output: Output, expected_messages):
     return __check_string_msg(output.stderr, expected_messages)