Add failing test case for unicode command in PY2

Author: myw

tests/test_common.py

@@ -160,6 +160,10 @@ def test_tmux_cmd_raises_on_not_found():
     tmux_cmd('-V')
 
 
+def test_tmux_cmd_unicode():
+    tmux_cmd('has-session', 'юникод')
+
+
 @pytest.mark.parametrize("session_name,raises,exc_msg_regex", [
     ('', True, 'may not be empty'),
     (None, True, 'may not be empty'),