test: cover missing branches in sphinx_ext.py and extract.py

Add tests for the :name: directive option on Mermaid format (with and
without caption).  Mark the defensive dedup guard in _format_event_names
as pragma: no branch since Events already deduplicates at the container
level.

Author: fgmacedo

statemachine/contrib/diagram/extract.py

@@ -123,7 +123,7 @@ def _format_event_names(transition: "Transition") -> str:
         # form ("done_invoke_X") is also registered on this transition.
         if "." in eid and eid.replace(".", "_") in all_ids:
             continue
-        if eid not in display:
+        if eid not in display:  # pragma: no branch
             display.append(eid)
 
     return " ".join(display)

tests/test_contrib_diagram.py

@@ -1737,6 +1737,22 @@ def test_mermaid_format_with_caption(self, tmp_path):
         assert len(caption_children) == 1
         assert caption_children[0].astext() == "My Diagram"
 
+    def test_mermaid_format_with_caption_and_name(self, tmp_path):
+        """Mermaid format with caption and :name: calls add_name on the figure."""
+        _, result = self._run(
+            tmp_path, options={"format": "mermaid", "caption": "My Diagram", "name": "fig-sm"}
+        )
+        assert len(result) == 1
+        assert isinstance(result[0], nodes.figure)
+
+    def test_mermaid_format_with_name_no_caption(self, tmp_path):
+        """Mermaid format with :name: but no caption calls add_name on the mermaid node."""
+        from sphinxcontrib.mermaid import mermaid as MermaidNode  # type: ignore[import-untyped]
+
+        _, result = self._run(tmp_path, options={"format": "mermaid", "name": "fig-sm"})
+        assert len(result) == 1
+        assert isinstance(result[0], MermaidNode)
+
     def test_mermaid_format_fallback_no_sphinxcontrib(self, tmp_path):
         """When sphinxcontrib-mermaid is not available, falls back to code block."""
         import sys