pretend a root_dir is defined for this test

tests/test_mpsd_software.py

@@ -575,6 +575,11 @@ def test_get_available_releases():
 def test_argument_line_parsing(mocker):
     """Check to find error in argparse logic"""
 
+    # pretend we have a rootdir defined
+    mock = mocker.patch(
+        "mpsd_software_manager.mpsd_software.get_root_dir", return_value=Path(".")
+    )
+
     ### available
     sys.argv = ["mpsd-software-tests", "available"]
     mock = mocker.patch(