diff --git a/tools/chat-filter/tests/test_filter_chats.py b/tools/chat-filter/tests/test_filter_chats.py
new file mode 100644
index 0000000..b21cf4d
--- /dev/null
+++ b/tools/chat-filter/tests/test_filter_chats.py
@@ -0,0 +1,46 @@
+import sys
+from pathlib import Path
+
+# Add path to import filter_chats module
+sys.path.append(str(Path(__file__).resolve().parent.parent))
+from filter_chats import extract_from_mapping, compile_scrubs, scrub_text
+
+
+def test_extract_from_mapping():
+    row = {
+        "mapping": {
+            "first": {
+                "message": {
+                    "create_time": 111,
+                    "content": {"parts": ["hello"]},
+                    "metadata": {"model_slug": "gpt-4"},
+                    "author": {"role": "assistant"},
+                }
+            },
+            "second": {
+                "message": {
+                    "create_time": 222,
+                    "content": {"parts": ["hi", "there"]},
+                    "author": {"role": "user"},
+                }
+            },
+        }
+    }
+
+    expected = [
+        {"timestamp": 111, "model": "gpt-4", "text": "hello"},
+        {"timestamp": 222, "model": "user", "text": "hi\nthere"},
+    ]
+    assert extract_from_mapping(row) == expected
+
+
+def test_scrub_text():
+    scrubs = compile_scrubs(
+        [
+            {"pattern": r"secret", "replace": "[redacted]"},
+            {"pattern": r"\d+", "replace": "#"},
+        ]
+    )
+    original = "secret code 1234"
+    assert scrub_text(original, scrubs) == "[redacted] code #"
+