diff --git a/report_generator/tests/test_core.py b/report_generator/tests/test_core.py
new file mode 100644
index 0000000..87ed517
--- /dev/null
+++ b/report_generator/tests/test_core.py
@@ -0,0 +1,85 @@
+import json
+import os
+from pathlib import Path
+import pytest
+
+# Da der Modulname im api_contract 'core' ist und das Paket report_generator heißt
+from report_generator import core
+
+
+@pytest.fixture
+def tmp_output(monkeypatch, tmp_path):
+    output_path = tmp_path / 'drift_report.json'
+    # monkeypatch output path if used inside core
+    monkeypatch.setattr(core.Path, 'cwd', lambda: tmp_path)
+    return output_path
+
+
+def load_report(path: str) -> dict:
+    with open(path, 'r', encoding='utf-8') as fh:
+        return json.load(fh)
+
+
+@pytest.mark.parametrize(
+    "warn_count,total_runs,threshold,expected_alert",
+    [
+        (1, 10, 0.3, False),  # warn_rate < threshold
+        (3, 10, 0.3, False),  # warn_rate == threshold (0.3)
+        (4, 10, 0.3, True),   # warn_rate > threshold
+    ]
+)
+def test_generate_report_threshold_logic(tmp_path, warn_count, total_runs, threshold, expected_alert):
+    # invoke function
+    report_path = core.generate_report(warn_count, total_runs, threshold)
+
+    # output verification
+    assert isinstance(report_path, str), "generate_report should return path as string"
+    assert os.path.exists(report_path), f"Report file {report_path} does not exist"
+
+    # check JSON structure
+    report = load_report(report_path)
+
+    # Required fields in DriftReport according to data_models
+    for field in ["warn_rate", "threshold", "alert", "timestamp"]:
+        assert field in report, f"Missing field: {field}"
+
+    # semantic checks
+    expected_rate = pytest.approx(warn_count / total_runs)
+    assert report["warn_rate"] == expected_rate
+    assert float(report["threshold"]) == threshold
+    assert bool(report["alert"]) == expected_alert
+
+
+def test_generate_report_invalid_input_types():
+    with pytest.raises((AssertionError, ValueError, TypeError)):
+        core.generate_report('warns', 10, 0.3)
+
+    with pytest.raises((AssertionError, ValueError, TypeError)):
+        core.generate_report(5, 'total', 0.3)
+
+    with pytest.raises((AssertionError, ValueError, TypeError)):
+        core.generate_report(2, 5, 'threshold')
+
+
+def test_generate_report_zero_total():
+    with pytest.raises((ZeroDivisionError, ValueError, AssertionError)):
+        core.generate_report(1, 0, 0.3)
+
+
+def test_generate_report_file_content_consistency(tmp_path):
+    warn_count, total_runs, threshold = 2, 10, 0.2
+    path = core.generate_report(warn_count, total_runs, threshold)
+    data = load_report(path)
+
+    # check timestamp format ISO-like
+    assert isinstance(data["timestamp"], str)
+    assert 'T' in data["timestamp"], "timestamp should be in ISO format"
+
+    # check global consistency
+    assert pytest.approx(data["warn_rate"], rel=1e-6) == warn_count / total_runs
+    assert data["threshold"] == threshold
+    assert isinstance(data["alert"], bool)
+
+    # Cleanup for CI safety
+    os.remove(path)
+    assert not os.path.exists(path)
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