Deprecate support for passing command-line as string to pytest.main()

Fixes #1723

CHANGELOG.rst

@@ -203,6 +203,9 @@ time or change existing behaviors in order to make them less surprising/more use
  removed in pytest-4.0 (`#1684`_).
  Thanks `@nicoddemus`_ for the PR.
 
+* Passing a command-line string to ``pytest.main()`` is considered deprecated and scheduled
+ for removal in pytest-4.0. It is recommended to pass a list of arguments instead (`#1723`_).
+
 * Rename ``getfuncargvalue`` to ``getfixturevalue``. ``getfuncargvalue`` is
  still present but is now considered deprecated. Thanks to `@RedBeardCode`_ and `@tomviner`_
  for the PR (`#1626`_).
@@ -282,6 +285,7 @@ time or change existing behaviors in order to make them less surprising/more use
 .. _#1633: https://github.com/pytest-dev/pytest/pull/1633
 .. _#1664: https://github.com/pytest-dev/pytest/pull/1664
 .. _#1684: https://github.com/pytest-dev/pytest/pull/1684
+.. _#1723: https://github.com/pytest-dev/pytest/pull/1723
 
 .. _@DRMacIver: https://github.com/DRMacIver
 .. _@RedBeardCode: https://github.com/RedBeardCode

_pytest/config.py

@@ -98,6 +98,7 @@ def get_plugin_manager():
  return get_config().pluginmanager
 
 def _prepareconfig(args=None, plugins=None):
+ warning = None
  if args is None:
  args = sys.argv[1:]
  elif isinstance(args, py.path.local):
@@ -106,6 +107,10 @@ def _prepareconfig(args=None, plugins=None):
  if not isinstance(args, str):
  raise ValueError("not a string or argument list: %r" % (args,))
  args = shlex.split(args, posix=sys.platform != "win32")
+ # we want to remove this way of passing arguments to pytest.main()
+ # in pytest-4.0
+ warning = ('passing a string to pytest.main() is deprecated, '
+ 'pass a list of arguments instead.')
  config = get_config()
  pluginmanager = config.pluginmanager
  try:
@@ -115,6 +120,8 @@ def _prepareconfig(args=None, plugins=None):
  pluginmanager.consider_pluginarg(plugin)
  else:
  pluginmanager.register(plugin)
+ if warning:
+ config.warn('C1', warning)
  return pluginmanager.hook.pytest_cmdline_parse(
  pluginmanager=pluginmanager, args=args)
  except BaseException:

testing/acceptance_test.py

@@ -795,3 +795,17 @@ def test_funcarg_prefix(value):
  'Please remove the prefix and use the @pytest.fixture decorator instead.'),
  '*1 passed*',
  ])
+
+
+def test_str_args_deprecated(tmpdir, testdir):
+ """Deprecate passing strings to pytest.main(). Scheduled for removal in pytest-4.0."""
+ warnings = []
+
+ class Collect:
+ def pytest_logwarning(self, message):
+ warnings.append(message)
+
+ ret = pytest.main("%s -x" % tmpdir, plugins=[Collect()])
+ testdir.delete_loaded_modules()
+ assert warnings == ['passing a string to pytest.main() is deprecated, pass a list of arguments instead.']
+ assert ret == EXIT_NOTESTSCOLLECTED