MNT: Debug fig_size change after window close

Author: timhoffm

lib/matplotlib/tests/test_backends_interactive.py

@@ -216,11 +216,12 @@ def check_alt_backend(alt_backend):
     fig.canvas.mpl_connect("draw_event", lambda event: timer.start())
     fig.canvas.mpl_connect("close_event", print)
 
+    plt.show()
+
+    size_inches = fig.get_size_inches()
     result = io.BytesIO()
     fig.savefig(result, format='png')
 
-    plt.show()
-
     # Ensure that the window is really closed.
     plt.pause(0.5)
 
@@ -229,6 +230,8 @@ def check_alt_backend(alt_backend):
     result_after = io.BytesIO()
     fig.savefig(result_after, format='png')
 
+    assert tuple(fig.get_size_inches()) == tuple(size_inches), \
+        f"{fig.get_size_inches()}, {size_inches}"
     assert result.getvalue() == result_after.getvalue()