Tests: modern PEP8-ify core test modules and methods (#2298)

* rename modules

* rename methods

* add docstrings to the general tests

* add base import stub

* test_base -> bases

* print deprecation warning

* redo 2346

test/general/test_implemented.py

@@ -0,0 +1,33 @@
+import unittest
+from worlds.AutoWorld import AutoWorldRegister
+
+from . import setup_solo_multiworld
+
+
+class TestImplemented(unittest.TestCase):
+    def test_completion_condition(self):
+        """Ensure a completion condition is set that has requirements."""
+        for game_name, world_type in AutoWorldRegister.world_types.items():
+            if not world_type.hidden and game_name not in {"Sudoku"}:
+                with self.subTest(game_name):
+                    multiworld = setup_solo_multiworld(world_type)
+                    self.assertFalse(multiworld.completion_condition[1](multiworld.state))
+
+    def test_entrance_parents(self):
+        """Tests that the parents of created Entrances match the exiting Region."""
+        for game_name, world_type in AutoWorldRegister.world_types.items():
+            if not world_type.hidden:
+                with self.subTest(game_name):
+                    multiworld = setup_solo_multiworld(world_type)
+                    for region in multiworld.regions:
+                        for exit in region.exits:
+                            self.assertEqual(exit.parent_region, region)
+
+    def test_stage_methods(self):
+        """Tests that worlds don't try to implement certain steps that are only ever called as stage."""
+        for game_name, world_type in AutoWorldRegister.world_types.items():
+            if not world_type.hidden:
+                with self.subTest(game_name):
+                    for method in ("assert_generate",):
+                        self.assertFalse(hasattr(world_type, method),
+                                         f"{method} must be implemented as a @classmethod named stage_{method}.")