Warnings generated by pytest-xdist

While working on pytest-dev/pytest#2072 I noticed that pytest-xdist raises these warnings when running pytest's test suite:

• addoption receiving a string instead of a type:

  File "c:\pytest\.tox\py35-xdist\lib\site-packages\xdist\plugin.py", line 36, in pytest_addoption
    help=("set mode for distributing tests to exec environments.\n\n"
  File "C:\pytest\_pytest\config.py", line 752, in _addoption
    option = Argument(*optnames, **attrs)
  File "C:\pytest\_pytest\config.py", line 639, in __init__
    stacklevel=3)
  DeprecationWarning: type argument to addoption() is a string 'choice'. For parsearg this is optional and when supplied should be a type. (options: ('--dist',))
  

• inspect.getargspec on Python >= 3.5:

  INTERNALERROR>   File "c:\pytest\.tox\py35-xdist\lib\site-packages\execnet\gateway.py", line 186, in _source_of_function
  INTERNALERROR>     args, varargs, keywords, defaults = inspect.getargspec(function)
  INTERNALERROR>   File "c:\python35\Lib\inspect.py", line 1040, in getargspec
  INTERNALERROR>     stacklevel=2)
  INTERNALERROR> DeprecationWarning: inspect.getargspec() is deprecated, use inspect.signature() instead
  

Start by inspecting the pytest_addoption path in xdist/plugin.py and the _source_of_function path in execnet/gateway.py shown in the warning traces. Run pytest-xdist's test suite under Python 3.5 or newer and verify that the reported deprecation warnings no longer occur.