TST: make mosaic order test more pathological

Author: tacaswell

lib/matplotlib/tests/test_figure.py

@@ -870,12 +870,17 @@ def test_user_order(self, str_pattern):
         assert list(fig.axes) == list(ax_dict.values())
 
     def test_nested_user_order(self):
-        layout = [["A", [["B", "C"], ["D", "E"]]],
-                  ["F", "G"]]
+        layout = [
+            ["A", [["B", "C"],
+                   ["D", "E"]]],
+            ["F", "G"],
+            [".", [["H", [["I"],
+                          ["."]]]]]
+        ]
 
         fig = plt.figure()
         ax_dict = fig.subplot_mosaic(layout)
-        assert list(ax_dict) == list("ABCDEFG")
+        assert list(ax_dict) == list("ABCDEFGHI")
         assert list(fig.axes) == list(ax_dict.values())