fix(use_agg_backend):

agentic_security/report_chart.py

@@ -59,7 +59,6 @@ def _plot_security_report(table: Table) -> io.BytesIO:
     Returns:
         io.BytesIO: A buffer containing the generated plot image in PNG format.
     """
-    return io.BytesIO()
     # Data preprocessing
     logger.info("Data preprocessing started.")
 

tests/unit/test_report_chart.py

@@ -2,8 +2,7 @@ import io
 
 import matplotlib
 import pytest
-
-matplotlib.use("Agg")
+from inline_snapshot import snapshot
 
 from agentic_security.report_chart import (
     _generate_identifiers,
@@ -12,6 +11,11 @@ from agentic_security.report_chart import (
 )
 
 
+@pytest.fixture(autouse=True)
+def use_agg_backend():
+    matplotlib.use("Agg")
+
+
 class TestGenerateIdentifiers:
     def test_single_row(self):
         data = type("DF", (), {"__len__": lambda s: 1})()
@@ -58,7 +62,10 @@ class TestPlotSecurityReport:
             {"module": "mod_c", "failureRate": 25.0, "tokens": 500},
         ]
         result = plot_security_report(table_data)
-        assert result.getvalue() != b""
+        # A real plot was rendered: non-empty buffer carrying the PNG signature.
+        png = result.getvalue()
+        assert len(png) > 0
+        assert png[:8] == snapshot(b"\x89PNG\r\n\x1a\n")
 
     def test_handles_empty_data(self):
         result = plot_security_report([])