diff --git a/tests/components/tts/conftest.py b/tests/components/tts/conftest.py
index 43488808693..dd018e4673f 100644
--- a/tests/components/tts/conftest.py
+++ b/tests/components/tts/conftest.py
@@ -3,12 +3,13 @@
 From http://doc.pytest.org/en/latest/example/simple.html#making-test-result-information-available-in-fixtures
 """
 from collections.abc import Generator
+import os
 from typing import Any
 from unittest.mock import MagicMock, patch
 
 import pytest
 
-from homeassistant.components.tts import _get_cache_files
+from homeassistant.components.tts import DEFAULT_CACHE_DIR, _get_cache_files
 from homeassistant.config import async_process_ha_core_config
 from homeassistant.config_entries import ConfigFlow
 from homeassistant.core import HomeAssistant
@@ -49,9 +50,14 @@ def mock_get_cache_files():
 
 @pytest.fixture(autouse=True)
 def mock_init_cache_dir(
+    hass: HomeAssistant,
     init_cache_dir_side_effect: Any,
 ) -> Generator[MagicMock, None, None]:
-    """Mock the TTS cache dir in memory."""
+    """Prevent the TTS cache from being created and fail the test if it exists."""
+    cache_dir = hass.config.path(DEFAULT_CACHE_DIR)
+    if os.path.isdir(cache_dir):
+        pytest.fail(f"Default TTS cache dir '{cache_dir}' already exists")
+
     with patch(
         "homeassistant.components.tts._init_tts_cache_dir",
         side_effect=init_cache_dir_side_effect,