diff --git a/data_collection/tests/test_core.py b/data_collection/tests/test_core.py
new file mode 100644
index 0000000..173d13e
--- /dev/null
+++ b/data_collection/tests/test_core.py
@@ -0,0 +1,45 @@
+import pytest
+import time
+from datetime import datetime, timezone
+from data_collection import core
+
+
+def test_collect_run_data_structure_and_types():
+    result = core.collect_run_data(run_id=1, worker_count=2)
+    assert isinstance(result, dict), "Return type muss dict sein"
+
+    expected_fields = {"epoch_ms": int, "monotonic_ns": int, "tz_offset_minutes": int, "retry_tail_p99": float, "band_width": float}
+    for field, ftype in expected_fields.items():
+        assert field in result, f"Feld {field} fehlt im Ergebnis"
+        assert isinstance(result[field], ftype), f"Feld {field} muss Typ {ftype.__name__} haben"
+
+
+def test_epoch_ms_reasonable_range():
+    result = core.collect_run_data(run_id=5, worker_count=1)
+    now_ms = int(time.time() * 1000)
+    assert abs(result["epoch_ms"] - now_ms) < 1000 * 5, "epoch_ms sollte aktueller Zeit entsprechen"
+
+
+def test_monotonic_ns_increasing():
+    first = core.collect_run_data(run_id=2, worker_count=3)
+    time.sleep(0.001)
+    second = core.collect_run_data(run_id=2, worker_count=3)
+    assert second["monotonic_ns"] > first["monotonic_ns"], "monotonic_ns sollte mit der Zeit steigen"
+
+
+def test_tz_offset_nonzero_or_known():
+    result = core.collect_run_data(run_id=3, worker_count=4)
+    assert isinstance(result["tz_offset_minutes"], int)
+    assert -720 <= result["tz_offset_minutes"] <= 840, "tz_offset_minutes sollte gültiger Offset sein"
+
+
+def test_retry_tail_p99_and_bandwidth_values():
+    result = core.collect_run_data(run_id=10, worker_count=5)
+    assert result["retry_tail_p99"] >= 0.0, "retry_tail_p99 sollte positiv sein"
+    assert result["band_width"] > 0.0, "band_width sollte > 0 sein"
+
+
+def test_multiple_invocations_yield_distinct_results():
+    r1 = core.collect_run_data(run_id=11, worker_count=1)
+    r2 = core.collect_run_data(run_id=11, worker_count=1)
+    assert r1 != r2, "Zwei Messungen sollten sich unterscheiden (Zeit)"