diff --git a/heatmap_visualization/tests/test_core.py b/heatmap_visualization/tests/test_core.py
new file mode 100644
index 0000000..4c63f9a
--- /dev/null
+++ b/heatmap_visualization/tests/test_core.py
@@ -0,0 +1,39 @@
+import pytest
+import pandas as pd
+import matplotlib.figure as mfig
+import seaborn as sns
+from heatmap_visualization import core
+
+@pytest.fixture
+def sample_log_data():
+    # Beispielhafte Logdaten inklusive Edge-Case (Nullwerte, Varianz)
+    return pd.DataFrame([
+        {"worker_start_offset": 0.0, "expires_at_dist_hours": 12.0, "retry_total_overhead_ms": 150.0},
+        {"worker_start_offset": 1.5, "expires_at_dist_hours": 8.0, "retry_total_overhead_ms": 300.0},
+        {"worker_start_offset": 3.0, "expires_at_dist_hours": 10.0, "retry_total_overhead_ms": 120.0},
+        {"worker_start_offset": 0.5, "expires_at_dist_hours": 7.5, "retry_total_overhead_ms": 200.0},
+        {"worker_start_offset": 2.0, "expires_at_dist_hours": 9.0, "retry_total_overhead_ms": 180.0}
+    ])
+
+def test_generate_heatmap_returns_figure(sample_log_data):
+    fig = core.generate_heatmap(sample_log_data)
+    assert isinstance(fig, mfig.Figure), "Erwartet ein Matplotlib Figure-Objekt"
+
+def test_generate_heatmap_with_list_input(sample_log_data):
+    data_list = sample_log_data.to_dict(orient="records")
+    fig = core.generate_heatmap(data_list)
+    assert isinstance(fig, mfig.Figure)
+
+def test_generate_heatmap_invalid_input():
+    with pytest.raises((ValueError, TypeError)):
+        core.generate_heatmap({"not": "valid"})
+
+def test_heatmap_visualization_colormap(sample_log_data):
+    fig = core.generate_heatmap(sample_log_data)
+    # Überprüfe, ob Seaborn-Heatmap-Farbschema korrekt angewendet wurde.
+    assert any(ax.images for ax in fig.axes), "Heatmap enthält kein Farb-Image"
+
+@pytest.mark.parametrize("invalid_data", [None, [], [{}], [{"worker_start_offset": None}]])
+def test_generate_heatmap_edge_cases(invalid_data):
+    with pytest.raises((ValueError, TypeError)):
+        core.generate_heatmap(invalid_data)
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