diff --git a/generate_report/tests/test_core.py b/generate_report/tests/test_core.py
new file mode 100644
index 0000000..e6b35e0
--- /dev/null
+++ b/generate_report/tests/test_core.py
@@ -0,0 +1,72 @@
+import pytest
+from datetime import datetime
+from generate_report import core
+
+
+def example_latency_results():
+    return [
+        {
+            "batch_id": "b1",
+            "metric": "p50",
+            "value_ms": 120.5,
+            "timestamp": datetime(2024, 1, 1, 12, 0, 0).isoformat(),
+        },
+        {
+            "batch_id": "b1",
+            "metric": "p95",
+            "value_ms": 145.2,
+            "timestamp": datetime(2024, 1, 1, 12, 0, 10).isoformat(),
+        },
+    ]
+
+
+def example_analysis_summary():
+    return {
+        "batch_count": 1,
+        "avg_latency": 132.85,
+        "max_latency": 145.2,
+        "drift_detected": False,
+    }
+
+
+def test_create_report_nominal():
+    latency_results = example_latency_results()
+    analysis_summary = example_analysis_summary()
+
+    report = core.create_report(latency_results, analysis_summary)
+
+    assert isinstance(report, dict)
+    assert "title" in report
+    assert "created_at" in report
+    assert "summary_text" in report
+    assert "metrics" in report
+
+    assert report["title"] == "Batch Latency Measurement Report"
+    assert any(m["metric"] == "p50" for m in report["metrics"])
+
+
+def test_create_report_empty_inputs():
+    report = core.create_report([], {})
+    assert isinstance(report, dict)
+    assert report["metrics"] == []
+
+
+def test_create_report_type_validation():
+    with pytest.raises((TypeError, ValueError)):
+        core.create_report("not_a_list", example_analysis_summary())
+    with pytest.raises((TypeError, ValueError)):
+        core.create_report(example_latency_results(), "not_a_dict")
+
+
+def test_create_report_summary_content():
+    latency_results = example_latency_results()
+    analysis_summary = example_analysis_summary()
+
+    report = core.create_report(latency_results, analysis_summary)
+    summary_text = report.get("summary_text", "")
+
+    assert str(analysis_summary["avg_latency"]) in summary_text
+    if analysis_summary["drift_detected"]:
+        assert "drift" in summary_text.lower()
+    else:
+        assert "drift" not in summary_text.lower()