[BUG] ValueError when using --test-differ

[Markus00000]

Describe the bug.
Using --test-differ as documented online and in webchanges -h results in a ValueError.

$ webchanges -v --test-differ 4
2024-04-23 16:04:03,558 cli[126289157486400] INFO: webchanges: 3.21 Copyright 2020- Mike Borsetti
2024-04-23 16:04:03,558 cli[126289157486400] INFO: CPython: 3.11.8 ('main', 'Feb 12 2024 14:50:05') GCC 13.2.1 20230801
2024-04-23 16:04:03,558 cli[126289157486400] INFO: System: Linux-6.8.7-arch1-1-x86_64-with-glibc2.39
2024-04-23 16:04:03,840 storage[126289157486400] INFO: The configuration file /home/m/.config/webchanges/config.yaml is missing directive(s); the following default values are being used:
database:
  engine: sqlite3
  max_snapshots: 4
display:
  empty-diff: true
  error: true
  new: true
  unchanged: false
footnote: null
report:
  browser:
    enabled: false
  discord:
    colored: true
    embed: true
    enabled: false
    max_message_length: null
    subject: '[webchanges] {count} changes{jobs_files}: {jobs}'
    webhook_url: ''
  email:
    enabled: false
    from: ''
    html: true
    method: smtp
    sendmail:
      path: sendmail
    smtp:
      auth: true
      host: localhost
      insecure_password: ''
      port: 25
      starttls: true
      user: ''
    subject: '[webchanges] {count} changes{jobs_files}: {jobs}'
    to: ''
  html:
    diff: unified
    footer: true
    separate: false
    title: '[webchanges] {count} changes{jobs_files}: {jobs}'
  ifttt:
    enabled: false
    event: ''
    key: ''
  mailgun:
    api_key: ''
    domain: ''
    enabled: false
    from_mail: ''
    from_name: ''
    region: us
    subject: '[webchanges] {count} changes{jobs_files}: {jobs}'
    to: ''
  markdown:
    details: true
    footer: true
    minimal: false
    separate: false
  matrix:
    access_token: ''
    enabled: false
    homeserver: ''
    room_id: ''
  prowl:
    api_key: ''
    application: ''
    enabled: false
    priority: 0
    subject: '[webchanges] {count} changes{jobs_files}: {jobs}'
  pushbullet:
    api_key: ''
    enabled: false
  pushover:
    app: ''
    device: null
    enabled: false
    priority: normal
    sound: spacealarm
    user: ''
  run_command:
    command: ''
    enabled: false
  stdout:
    color: true
    enabled: true
  telegram:
    bot_token: ''
    chat_id: ''
    enabled: false
    silent: false
  text:
    details: true
    footer: true
    line_length: 75
    minimal: false
    separate: false
  tz: null
  webhook:
    enabled: false
    markdown: false
    max_message_length: null
    rich_text: null
    webhook_url: ''
  xmpp:
    enabled: false
    insecure_password: ''
    recipient: ''
    sender: ''
See documentation at https://webchanges.readthedocs.io/en/stable/configuration.html
2024-04-23 16:04:03,840 storage[126289157486400] INFO: Loaded configuration from /home/m/.config/webchanges/config.yaml
2024-04-23 16:04:03,841 storage[126289157486400] INFO: Using sqlite3 3.45.3 database at /home/m/.cache/webchanges/cache.db
2024-04-23 16:04:03,861 storage[126289157486400] INFO: Loaded 67 jobs from [PosixPath('/home/m/.config/webchanges/jobs.yaml')]
Traceback (most recent call last):
  File "/usr/bin/webchanges", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/usr/lib/python3.11/site-packages/webchanges/cli.py", line 392, in main
    urlwatch_command.run()
  File "/usr/lib/python3.11/site-packages/webchanges/command.py", line 1097, in run
    self.handle_actions()
  File "/usr/lib/python3.11/site-packages/webchanges/command.py", line 1034, in handle_actions
    self._exit(self.test_differ(self.urlwatch_config.test_differ))
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/webchanges/command.py", line 478, in test_differ
    job_id, max_diffs_str = arg_test_differ
    ^^^^^^^^^^^^^^^^^^^^^
ValueError: not enough values to unpack (expected 2, got 1)

Supplying the second argument works:

$ webchanges -v --test-differ 4 1

Expected behavior.
Document the second argument. If no second argument is given, diff snapshots 0 and -1. Currently the second argument is [JOB ...]. I expected --test-differ JOB [NUM_DIFFS].

Related: When more diffs are requested than are available, the output is IndexError: list index out of range. Maybe consider catching the exception and output something like No more snapshots found or No more diffs available.

Version info.

$ webchanges --detailed-versions
Software:
• webchanges: 3.21
• CPython: 3.11.8 ('main', 'Feb 12 2024 14:50:05') GCC 13.2.1 20230801
• SQLite: 3.45.3

System:
• Platform: Linux-6.8.7-arch1-1-x86_64-with-glibc2.39, x86_64
• Processor: 
• CPUs (logical): 12
• Free memory: 7.6G physical plus 15.2G swap.
• Free disk '/': 16.3G (23.8%)

Installed PyPi dependencies:
• beautifulsoup4: 4.12.3
• colorama: 0.4.6
• cryptography: 42.0.5
  - cffi: 1.16.0
  - mypy: 1.9.0
  - click: 8.1.7
  - build: 0.10.0
  - bcrypt: 4.1.2
  - certifi: 2024.2.2
• cssselect: 1.2.0
• html2text: 2020.1.16
• html5lib: 1.1
  - webencodings: 0.5.1
• httpx: 0.26.0
  - anyio: 4.3.0
  - certifi: 2024.2.2
  - idna: 3.6
  - sniffio: 1.3.1
• keyring: 25.0.0
  - jaraco.classes: 3.3.1
  - jaraco.functools: 3.7.0
  - jaraco.context: 4.3.0
  - importlib-metadata: 5.1.0
  - SecretStorage: 3.3.3
  - jeepney: 0.8.0
  - shtab: 1.6.5
• lxml: 5.1.0
• markdown2: 2.4.12
• msgpack: 1.0.5
• pdftotext: 2.2.2
• Pillow: 10.3.0
  - coverage: 7.4.1
  - markdown2: 2.4.12
  - packaging: 23.2
  - typing-extensions: 4.10.0
• platformdirs: 4.2.0
• playwright: 1.43.0
  - greenlet: 3.0.3
  - pyee: 11.0.1
• psutil: 5.9.8
• pyyaml: 6.0.1
• requests: 2.31.0
  - charset-normalizer: 3.3.2
  - idna: 3.6
  - urllib3: 1.26.18
  - chardet: 5.2.0
• tzdata: 2024.1
• vobject: 0.9.7
  - python-dateutil: 2.9.0
playwright._impl._errors.Error: BrowserType.launch: Chromium distribution 'chrome' is not found at /opt/google/chrome/chrome
Run "playwright install chrome"

[mborsetti]

Thanks for the report, and will fix in the next few hours.

[mborsetti]

Fixed in 3.22, just released.