diff --git a/tests/test_collector.py b/tests/test_collector.py
new file mode 100644
index 0000000..ba7aba1
--- /dev/null
+++ b/tests/test_collector.py
@@ -0,0 +1,33 @@
+import importlib.util
+from pathlib import Path
+
+spec = importlib.util.spec_from_file_location("collector", Path(__file__).parents[1] / "collector.py")
+c = importlib.util.module_from_spec(spec)
+spec.loader.exec_module(c)
+
+
+def test_scalar_values():
+    assert c.extract_values(b"21.5") == {"value": 21.5}
+    assert c.extract_values(b"ON") == {"value": 1.0}
+    assert c.extract_values(b"offline") == {"value": 0.0}
+
+
+def test_json_is_flattened_and_sensitive_fields_are_removed():
+    values = c.extract_values(b'{"temperature":21.2,"battery":88,"location":{"lat":48.1,"lon":11.5},"token":123,"online":true}')
+    assert values == {"temperature": 21.2, "battery": 88.0, "online": 1.0}
+
+
+def test_strings_and_binary_payloads_are_not_stored():
+    assert c.extract_values(b"Sascha ist zuhause") == {}
+    assert c.extract_values(b"\xff\x00") == {}
+
+
+def test_topic_policy():
+    assert c.topic_allowed("zigbee2mqtt/sensor/temperature")
+    assert not c.topic_allowed("camera/front/image")
+    assert not c.topic_allowed("homeassistant/sensor/foo/config")
+
+
+def test_line_protocol_escaping():
+    line = c.line("mqtt value", {"topic": "room, one"}, {"value": 1.5}, 123)
+    assert line == "mqtt\\ value,topic=room\\,\\ one value=1.5 123"