fix: changelog and update test list

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

docs/changelog/3446.feature.rst

@@ -0,0 +1,3 @@
+Add a ``schema`` command to produce a JSON Schema for tox and the current plugins.
+
+- by :user:`henryiii`

src/tox/session/cmd/schema.py

@@ -6,7 +6,6 @@
 import sys
 import typing
 from pathlib import Path
-from types import NoneType
 from typing import TYPE_CHECKING
 
 import packaging.requirements
@@ -39,7 +38,7 @@ def _process_type(of_type: typing.Any) -> dict[str, typing.Any]:  # noqa: C901,
     }:
         return {"type": "string"}
     if typing.get_origin(of_type) is typing.Union:
-        types = [x for x in typing.get_args(of_type) if x is not NoneType]
+        types = [x for x in typing.get_args(of_type) if x is not type(None)]
         if len(types) == 1:
             return _process_type(types[0])
         msg = f"Union types are not supported: {of_type}"

tests/config/cli/conftest.py

@@ -13,6 +13,7 @@
 from tox.session.cmd.run.parallel import run_parallel
 from tox.session.cmd.run.sequential import run_sequential
 from tox.session.cmd.show_config import show_config
+from tox.session.cmd.schema import gen_schema
 
 if TYPE_CHECKING:
     from tox.session.state import State
@@ -23,6 +24,7 @@ def core_handlers() -> dict[str, Callable[[State], int]]:
     return {
         "config": show_config,
         "c": show_config,
+        "schema": gen_schema,
         "list": list_env,
         "l": list_env,
         "run": run_sequential,