Differentiate dummy SVG vs PNG output when UNITTEST_GOING=1, both contain DISABLED FOR TESTS

Copilot · xadupre · Copilot · commit 30bbe655d724 · 2026-03-06T14:43:08.000Z
Co-authored-by: xadupre &lt;22452781+xadupre@users.noreply.github.com&gt;
diff --git a/_unittests/ut_gdot/test_gdot_extension.py b/_unittests/ut_gdot/test_gdot_extension.py
@@ -164,7 +164,7 @@ def test_gdot4_png(self):
 
     @ignore_warnings(PendingDeprecationWarning)
     def test_gdot_unittest_going_svg(self):
-        """When UNITTEST_GOING=1, a dummy SVG is rendered instead of calling graphviz."""
+        """When UNITTEST_GOING=1, a dummy SVG containing 'DISABLED FOR TESTS' is rendered."""
         content = """
                     before
 
@@ -183,12 +183,13 @@ def test_gdot_unittest_going_svg(self):
                 content, writer_name="html", new_extensions=["sphinx_runpython.gdot"]
             )
 
-        self.assertIn("dummy", html)
-        self.assertIn("svg", html)
+        self.assertIn("DISABLED FOR TESTS", html)
+        self.assertIn("<svg", html)
+        self.assertNotIn("<img", html)
 
     @ignore_warnings(PendingDeprecationWarning)
     def test_gdot_unittest_going_png(self):
-        """When UNITTEST_GOING=1, a dummy SVG is rendered for png format too."""
+        """When UNITTEST_GOING=1, a dummy image containing 'DISABLED FOR TESTS' is rendered."""
         content = """
                     before
 
@@ -207,8 +208,9 @@ def test_gdot_unittest_going_png(self):
                 content, writer_name="html", new_extensions=["sphinx_runpython.gdot"]
             )
 
-        self.assertIn("dummy", html)
-        self.assertIn("svg", html)
+        self.assertIn("DISABLED FOR TESTS", html)
+        self.assertIn("<img", html)
+        self.assertNotIn("<svg", html)
 
 
 if __name__ == "__main__":
diff --git a/sphinx_runpython/gdot/sphinx_gdot_extension.py b/sphinx_runpython/gdot/sphinx_gdot_extension.py
@@ -218,15 +218,23 @@ def depart_gdot_node_rst(self, node):
 
 _DUMMY_SVG = (
     '<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100">'
-    '<text x="10" y="50">dummy</text>'
+    '<text x="10" y="50">DISABLED FOR TESTS</text>'
     "</svg>"
 )
 
+_DUMMY_PNG_HTML = (
+    '<img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAC0lEQVQI12NgAAIABQ'
+    'AABjkB6QAAAABJRU5ErkJggg==" alt="DISABLED FOR TESTS" />'
+)
+
 
-def _emit_dummy_svg(self):
-    """Emit a placeholder SVG when ``UNITTEST_GOING=1`` is set."""
+def _emit_dummy_output(self, format: str = "svg"):
+    """Emit a placeholder graphic when ``UNITTEST_GOING=1`` is set."""
     self.body.append('<div class="graphviz">')
-    self.body.append(_DUMMY_SVG)
+    if format == "png":
+        self.body.append(_DUMMY_PNG_HTML)
+    else:
+        self.body.append(_DUMMY_SVG)
     self.body.append("</div>\n")
     raise nodes.SkipNode
 
@@ -243,7 +251,7 @@ def render_dot_html(
     format: str = "svg",
 ) -> tuple[str, str]:
     if os.environ.get("UNITTEST_GOING", "0") == "1":
-        _emit_dummy_svg(self)
+        _emit_dummy_output(self, format=format)
 
     if format not in {"png", "svg"}:
         logger = logging.getLogger(__name__)
@@ -381,7 +389,7 @@ def visit_gdot_node_html(self, node):
     """
     if node["format"].lower() == "png":
         if os.environ.get("UNITTEST_GOING", "0") == "1":
-            _emit_dummy_svg(self)
+            _emit_dummy_output(self, format="png")
         from sphinx.ext.graphviz import html_visit_graphviz
 
         return html_visit_graphviz(self, node)
