diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..620e26c
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,16 @@
+"""Shared pytest configuration for the snake game tests."""
+
+from pathlib import Path
+
+import pytest
+
+
+@pytest.fixture(autouse=True)
+def isolated_working_directory(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
+    """Run every test in an empty temporary working directory.
+
+    The high score file has a relative default path (`data.txt`). Without this
+    fixture, a test that uses the default would read and write the real file of
+    the repository or of the directory pytest was started from.
+    """
+    monkeypatch.chdir(tmp_path)
diff --git a/tests/test_main.py b/tests/test_main.py
index 60aaed6..0c11448 100644
--- a/tests/test_main.py
+++ b/tests/test_main.py
@@ -1,5 +1,7 @@
 """Tests of the main flow, with fakes instead of a real screen."""
 
+from pathlib import Path
+
 import pytest
 
 from fakes import (
@@ -131,6 +133,16 @@ def test_main_sets_up_the_screen_turns_off_drawing_and_binds_the_keys(
     assert sorted(screens[0].bindings) == sorted(ARROW_KEYS)
 
 
+def test_main_creates_data_txt_in_the_working_directory_holding_0(
+    monkeypatch: pytest.MonkeyPatch, sleeps: list[float], tmp_path: Path
+) -> None:
+    install_fake_turtle(monkeypatch)
+
+    main()
+
+    assert (tmp_path / constants.HIGH_SCORE_FILE).read_text(encoding="utf-8") == "0"
+
+
 def test_register_head_shape_builds_two_components_from_the_constants(
     monkeypatch: pytest.MonkeyPatch,
 ) -> None: