main: args must be a list, not tuple (#6791)

Passing in a tuple crashes in `_prepareconfig`:

        def test_invoke_with_tuple(self):
    >       pytest.main(("-h",))

    src/_pytest/config/__init__.py:82: in main
        config = _prepareconfig(args, plugins)
    src/_pytest/config/__init__.py:229: in _prepareconfig
        return pluginmanager.hook.pytest_cmdline_parse(
    …
    src/_pytest/helpconfig.py:98: in pytest_cmdline_parse
        config = outcome.get_result()  # type: Config
    src/_pytest/config/__init__.py:808: in pytest_cmdline_parse
        self.parse(args)
    src/_pytest/config/__init__.py:1017: in parse
        self._preparse(args, addopts=addopts)
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

        def _preparse(self, args: List[str], addopts: bool = True) -> None:
            …
            if addopts:
                ini_addopts = self.getini("addopts")
                if ini_addopts:
    >               args[:] = self._validate_args(ini_addopts, "via addopts config") + args
    E               TypeError: can only concatenate list (not "tuple") to list

    addopts    = True
    args       = ('-h',)
    env_addopts = ''
    ini_addopts = ['-rfEX', …]

    src/_pytest/config/__init__.py:956: TypeError: can only concatenate list (not "tuple") to list

Might be worth handling (converting it to a list for example), but it
was documented to be a list to begin with when removing support for
strings (a7e4016).

Author: blueyed

src/_pytest/config/__init__.py

@@ -233,13 +233,15 @@ def get_plugin_manager():
     return get_config().pluginmanager
 
 
-def _prepareconfig(args=None, plugins=None):
+def _prepareconfig(
+    args: Optional[Union[py.path.local, List[str]]] = None, plugins=None
+):
     if args is None:
         args = sys.argv[1:]
     elif isinstance(args, py.path.local):
         args = [str(args)]
-    elif not isinstance(args, (tuple, list)):
-        msg = "`args` parameter expected to be a list or tuple of strings, got: {!r} (type: {})"
+    elif not isinstance(args, list):
+        msg = "`args` parameter expected to be a list of strings, got: {!r} (type: {})"
         raise TypeError(msg.format(args, type(args)))
 
     config = get_config(args, plugins)

testing/acceptance_test.py

@@ -606,7 +606,7 @@ def test_equivalence_pytest_pytest(self):
 
     def test_invoke_with_invalid_type(self):
         with pytest.raises(
-            TypeError, match="expected to be a list or tuple of strings, got: '-h'"
+            TypeError, match="expected to be a list of strings, got: '-h'"
         ):
             pytest.main("-h")