diff --git a/logger_setup/tests/test_core.py b/logger_setup/tests/test_core.py
new file mode 100644
index 0000000..dfd7e94
--- /dev/null
+++ b/logger_setup/tests/test_core.py
@@ -0,0 +1,76 @@
+import csv
+import os
+import tempfile
+import time
+from datetime import datetime
+
+import pytest
+
+import src.logger_setup.core as core
+
+
+@pytest.fixture
+def sample_reading():
+    ts = datetime.now()
+    return core.SensorReading(
+        timestamp=ts,
+        temperature=22.5,
+        humidity=55.0,
+        pressure=1013.25,
+        lux=150.0,
+    )
+
+
+def test_sensor_reading_to_dict_contains_expected_keys(sample_reading):
+    data = sample_reading.to_dict()
+    expected_keys = {"timestamp", "temperature", "humidity", "pressure", "lux"}
+    assert expected_keys.issubset(set(data.keys())), "All expected keys should be present."
+    assert isinstance(data["timestamp"], str) or isinstance(data["timestamp"], datetime)
+
+
+def test_save_to_csv_creates_valid_file(sample_reading):
+    with tempfile.TemporaryDirectory() as tmpdir:
+        csv_path = os.path.join(tmpdir, "sensor_log.csv")
+        # simulate data list like global buffer
+        if hasattr(core, "_data_buffer"):
+            core._data_buffer.clear()
+            core._data_buffer.append(sample_reading)
+        else:
+            # fallback for minimal implementation
+            core._data_buffer = [sample_reading]
+        core.save_to_csv(csv_path)
+        assert os.path.exists(csv_path)
+        with open(csv_path, newline="") as csvfile:
+            reader = csv.DictReader(csvfile)
+            rows = list(reader)
+            assert len(rows) == 1
+            row = rows[0]
+            assert float(row["temperature_c"]) == pytest.approx(22.5)
+            assert float(row["humidity_percent"]) == pytest.approx(55.0)
+            assert float(row["pressure_hpa"]) == pytest.approx(1013.25)
+            assert float(row["lux"]) == pytest.approx(150.0)
+
+
+def test_start_logging_runs_for_short_interval(monkeypatch):
+    calls = []
+
+    def fake_reading():
+        return core.SensorReading(datetime.now(), 20.0, 50.0, 1012.0, 100.0)
+
+    monkeypatch.setattr(core, "_read_sensors", fake_reading)
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+        csv_path = os.path.join(tmpdir, "sensor_log.csv")
+
+        def limited_sleep(duration):
+            calls.append(duration)
+            if len(calls) > 1:
+                raise KeyboardInterrupt
+
+        monkeypatch.setattr(time, "sleep", limited_sleep)
+        try:
+            core.start_logging(interval=0.1)
+        except KeyboardInterrupt:
+            pass
+
+    assert len(calls) >= 1, "start_logging should perform at least one loop iteration."
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