diff --git a/tests/unit/test_persistence.py b/tests/unit/test_persistence.py
new file mode 100644
index 0000000..8478b8c
--- /dev/null
+++ b/tests/unit/test_persistence.py
@@ -0,0 +1,171 @@
+from __future__ import annotations
+
+import json
+import tempfile
+import unittest
+from pathlib import Path
+
+from contribarena.engine.persistence import atomic_write_json, atomic_write_text
+
+
+class AtomicWriteTextTest(unittest.TestCase):
+    def test_writes_text_to_path(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "out.txt"
+
+            atomic_write_text(path, "hello")
+
+            self.assertEqual("hello", path.read_text(encoding="utf-8"))
+
+    def test_creates_missing_parent_directories(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "nested" / "deep" / "out.txt"
+
+            atomic_write_text(path, "data")
+
+            self.assertTrue(path.parent.is_dir())
+            self.assertEqual("data", path.read_text(encoding="utf-8"))
+
+    def test_overwrites_existing_file(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "out.txt"
+            path.write_text("old contents", encoding="utf-8")
+
+            atomic_write_text(path, "new contents")
+
+            self.assertEqual("new contents", path.read_text(encoding="utf-8"))
+
+    def test_preserves_non_ascii_characters_with_utf8(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "out.txt"
+
+            atomic_write_text(path, "caf\u00e9 \u2603 \U0001f600")
+
+            self.assertEqual(
+                "caf\u00e9 \u2603 \U0001f600",
+                path.read_text(encoding="utf-8"),
+            )
+
+    def test_does_not_leave_temp_file_after_success(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            parent = Path(tmp)
+            path = parent / "out.txt"
+
+            atomic_write_text(path, "data")
+
+            siblings = [p.name for p in parent.iterdir()]
+            self.assertEqual(["out.txt"], siblings)
+
+    def test_writes_empty_string(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "out.txt"
+
+            atomic_write_text(path, "")
+
+            self.assertTrue(path.exists())
+            self.assertEqual("", path.read_text(encoding="utf-8"))
+
+
+class AtomicWriteJsonTest(unittest.TestCase):
+    def test_writes_pretty_printed_json_with_trailing_newline(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "out.json"
+            payload = {"b": 1, "a": 2}
+
+            atomic_write_json(path, payload)
+
+            text = path.read_text(encoding="utf-8")
+            self.assertTrue(text.endswith("\n"))
+            self.assertEqual(payload, json.loads(text))
+
+    def test_indent_is_two_spaces(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "out.json"
+
+            atomic_write_json(path, {"key": "value"})
+
+            text = path.read_text(encoding="utf-8")
+            self.assertIn('\n  "key": "value"', text)
+
+    def test_sort_keys_true_sorts_keys_alphabetically(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "out.json"
+
+            atomic_write_json(path, {"b": 1, "a": 2, "c": 3}, sort_keys=True)
+
+            text = path.read_text(encoding="utf-8")
+            a_pos = text.index('"a"')
+            b_pos = text.index('"b"')
+            c_pos = text.index('"c"')
+            self.assertLess(a_pos, b_pos)
+            self.assertLess(b_pos, c_pos)
+
+    def test_sort_keys_false_by_default(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "out.json"
+
+            atomic_write_json(path, {"b": 1, "a": 2})
+
+            text = path.read_text(encoding="utf-8")
+            self.assertLess(text.index('"b"'), text.index('"a"'))
+
+    def test_ensure_ascii_true_escapes_non_ascii_by_default(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "out.json"
+
+            atomic_write_json(path, {"label": "caf\u00e9"})
+
+            text = path.read_text(encoding="utf-8")
+            self.assertIn("caf\\u00e9", text)
+            self.assertNotIn("caf\u00e9", text)
+            self.assertEqual({"label": "caf\u00e9"}, json.loads(text))
+
+    def test_ensure_ascii_false_preserves_non_ascii(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "out.json"
+
+            atomic_write_json(path, {"label": "caf\u00e9"}, ensure_ascii=False)
+
+            text = path.read_text(encoding="utf-8")
+            self.assertIn("caf\u00e9", text)
+            self.assertEqual({"label": "caf\u00e9"}, json.loads(text))
+
+    def test_creates_missing_parent_directories(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "nested" / "deep" / "out.json"
+
+            atomic_write_json(path, {"ok": True})
+
+            self.assertTrue(path.parent.is_dir())
+            self.assertEqual({"ok": True}, json.loads(path.read_text(encoding="utf-8")))
+
+    def test_overwrites_existing_file(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "out.json"
+            path.write_text("stale", encoding="utf-8")
+
+            atomic_write_json(path, {"fresh": True})
+
+            self.assertEqual({"fresh": True}, json.loads(path.read_text(encoding="utf-8")))
+
+    def test_writes_list_payload(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            path = Path(tmp) / "out.json"
+
+            atomic_write_json(path, [1, 2, 3])
+
+            self.assertEqual([1, 2, 3], json.loads(path.read_text(encoding="utf-8")))
+
+    def test_does_not_leave_temp_file_after_success(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            parent = Path(tmp)
+            path = parent / "out.json"
+
+            atomic_write_json(path, {"ok": True})
+
+            siblings = [p.name for p in parent.iterdir()]
+            self.assertEqual(["out.json"], siblings)
+
+
+if __name__ == "__main__":
+    unittest.main()