[tests] Clear testing_mode after every test (#21292)

tests/component_tests/conftest.py

@@ -55,6 +55,7 @@ def reset_core() -> Generator[None]:
     """Reset CORE after each test."""
     yield
     CORE.reset()
+    CORE.testing_mode = False  # reset() leaves it, so a test enabling it would leak
 
 
 @pytest.fixture(autouse=True)

tests/unit_tests/build_gen/test_arduino8266.py

@@ -62,8 +62,6 @@ def _setup_core(tmp_path: Path) -> Generator[None]:
         "build_src_flags": "-include esphome/components/esp8266/throw_stubs.h",
     }
     yield
-    # CORE.reset() (the suite-wide autouse fixture) does not clear this flag
-    CORE.testing_mode = False
 
 
 def _set_flags(*flags: str) -> None:

tests/unit_tests/conftest.py

@@ -48,6 +48,7 @@ def reset_core():
     """Reset CORE after each test."""
     yield
     CORE.reset()
+    CORE.testing_mode = False  # reset() leaves it, so a test enabling it would leak
 
 
 @pytest.fixture(autouse=True)