diff --git a/drift_data_collection/tests/test_core.py b/drift_data_collection/tests/test_core.py
new file mode 100644
index 0000000..eaf2f6d
--- /dev/null
+++ b/drift_data_collection/tests/test_core.py
@@ -0,0 +1,51 @@
+import json
+import pytest
+from datetime import datetime
+from pathlib import Path
+from drift_data_collection import core
+
+
+@pytest.fixture
+def sample_run_ids(tmp_path: Path):
+    file = tmp_path / "run_ids.json"
+    data = ["run_001", "run_002", "run_003"]
+    file.write_text(json.dumps(data))
+    return file, data
+
+
+def test_collect_frozen_runs_returns_list(sample_run_ids):
+    _, run_ids = sample_run_ids
+    result = core.collect_frozen_runs(run_ids)
+    assert isinstance(result, list)
+    # Ensure structure consistency
+    for item in result:
+        assert isinstance(item, dict)
+        assert set(["run_id", "status", "timestamp", "pinned_state", "metrics"]).issubset(item.keys())
+
+
+def test_collect_frozen_runs_content_valid(sample_run_ids):
+    _, run_ids = sample_run_ids
+    result = core.collect_frozen_runs(run_ids)
+    valid_statuses = {"PASS", "WARN", "FAIL"}
+    for run_data in result:
+        # Validate run_id
+        assert run_data["run_id"] in run_ids
+        # Validate allowed statuses
+        assert run_data["status"] in valid_statuses
+        # Validate timestamp format
+        ts = datetime.fromisoformat(run_data["timestamp"])
+        assert isinstance(ts, datetime)
+        # Validate pinned_state
+        assert isinstance(run_data["pinned_state"], bool)
+        # Validate metrics field
+        assert isinstance(run_data["metrics"], str)
+
+
+def test_collect_frozen_runs_empty_input():
+    result = core.collect_frozen_runs([])
+    assert result == []
+
+
+def test_collect_frozen_runs_invalid_input_type():
+    with pytest.raises((TypeError, AssertionError)):
+        core.collect_frozen_runs(None)  # type: ignore
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