pytest is not testing the command line arg parser correctly.

[jeffsilverm]

When I start pytest_3 with the debugger using the pytest_3 -x --psd test/test_nbmdt.py command, pytest_3 drops into pdb at /home/jeffs/python/nbmdt/test/test_nbmdt.py(174)test_debug_option(). syserr_str is:
`

/home/jeffs/python/nbmdt/test/test_nbmdt.py(174)test_debug_option()
-> assert "nominal " in syserr_str.lower(), """ "nominal " not found in syserr_str""" + "\n" + syserr_str
(Pdb) syserr_str
'Testing the file special variable: /home/jeffs/python/nbmdt/utilities.py\nTesting the file special variable: /home/jeffs/python/nbmdt/application.py\n\x1b[32mDebugging network.py: /bin/ip, /bin/ping, /bin/ping6\x1b[0m\nTesting the file special variable: /home/jeffs/python/nbmdt/nbmdt.py\nThe debug option was set. Mode is Modes.DIAGNOSE coded as 3\nProblems unpacking a line not enough values to unpack (expected 5, got 0) from the ps command: \n\nskip it\nqlen_str is not a valid int. It's \nif_str is 4: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default \ link/ether 02:42:02:fe:3e:9f brd ff:ff:ff:ff:ff:ff\n\nqlen_str is not a valid int. It's \nif_str is 19: vethc75b5727@if3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master cbr0 state UP mode DEFAULT group default \ link/ether 26:c6:9b:ff:ec:12 brd ff:ff:ff:ff:ff:ff link-netnsid 3\n\nqlen_str is not a valid int. It's \nif_str is 20: veth055373e3@if3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master cbr0 state UP mode DEFAULT group default \ link/ether 3e:cb:7d:f4:24:74 brd ff:ff:ff:ff:ff:ff link-netnsid 4\n\nqlen_str is not a valid int. It's \nif_str is 21: veth982b592e@if3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master cbr0 state UP mode DEFAULT group default \ link/ether 76:47:d5:7a:3c:98 brd ff:ff:ff:ff:ff:ff link-netnsid 2\n\nqlen_str is not a valid int. It's \nif_str is 22: vethdf72e796@if3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master cbr0 state UP mode DEFAULT group default \ link/ether de:61:f8:69:e5:5f brd ff:ff:ff:ff:ff:ff link-netnsid 5\n\nqlen_str is not a valid int. It's \nif_str is 23: veth13e9a885@if3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master cbr0 state UP mode DEFAULT group default \ link/ether fe:20:03:9f:e6:20 brd ff:ff:ff:ff:ff:ff link-netnsid 6\n\nqlen_str is not a valid int. It's \nif_str is 24: veth0cfe07e4@if3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master cbr0 state UP mode DEFAULT group default \ link/ether de:35:b0:08:3b:95 brd ff:ff:ff:ff:ff:ff link-netnsid 1\n\nqlen_str is not a valid int. It's \nif_str is 27: veth9b536b1f@if3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master cbr0 state UP mode DEFAULT group default \ link/ether 96:39:8a:e9:19:d7 brd ff:ff:ff:ff:ff:ff link-netnsid 0\n\nIn diagnostic mode, nomminal filename is mock_nbmdt_config.json\nTraceback (most recent call last):\n File "/home/jeffs/python/nbmdt/nbmdt.py", line 479, in \n main()\n File "/home/jeffs/python/nbmdt/nbmdt.py", line 313, in main\n current_system.diagnose(options.configuration_filename)\n File "/home/jeffs/python/nbmdt/nbmdt.py", line 272, in diagnose\n nominal_system: SystemDescription = SystemDescription.system_description_from_file(filename)\n File "/home/jeffs/python/nbmdt/nbmdt.py", line 119, in system_description_from_file\n so = json.load(f)\n File "/usr/lib/python3.6/json/init.py", line 299, in load\n parse_constant=parse_constant, object_pairs_hook=object_pairs_hook, **kw)\n File "/usr/lib/python3.6/json/init.py", line 354, in loads\n return _default_decoder.decode(s)\n File "/usr/lib/python3.6/json/decoder.py", line 339, in decode\n obj, end = self.raw_decode(s, idx=_w(s, 0).end())\n File "/usr/lib/python3.6/json/decoder.py", line 357, in raw_decode\n raise JSONDecodeError("Expecting value", s, err.value) from None\njson.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)\n'
(Pdb)

`
It looks to me as if syserr_str is getting appended to rather than overwritten.