tighten and comment test_never_update

richardsheridan · richardsheridan · commit 9bc82fb5d187 · 2020-08-11T11:20:29.000-04:00
diff --git a/lib/matplotlib/tests/test_backends_interactive.py b/lib/matplotlib/tests/test_backends_interactive.py
@@ -197,14 +197,30 @@ def test_webagg():
 
 
 @pytest.mark.backend('TkAgg', skip_on_importerror=True)
-def test_never_update(monkeypatch):
+def test_never_update(monkeypatch, capsys):
     import tkinter
     monkeypatch.delattr(tkinter.Misc, 'update')
     monkeypatch.delattr(tkinter.Misc, 'update_idletasks')
 
     import matplotlib.pyplot as plt
-    plt.plot([1, 2, 3], [1, 3, 5])
+    fig = plt.figure()
     plt.show(block=False)
-    fig = plt.gcf()
+
+    # regression test on FigureCanvasTkAgg
+    plt.draw()
+    # regression test on NavigationToolbar2Tk
     fig.canvas.toolbar.configure_subplots()
-    plt.pause(1e-9)
+
+    # check for update() or update_idletasks() in the event queue
+    # functionally equivalent to tkinter.Misc.update
+    # must pause >= 1 ms to process tcl idle events plus
+    # extra time to avoid flaky tests on slow systems
+    plt.pause(0.1)
+
+    # regression test on FigureCanvasTk filter_destroy callback
+    plt.close(fig)
+
+    # test framework doesn't see tkinter callback exceptions normally
+    # see tkinter.Misc.report_callback_exception
+    assert "Exception in Tkinter callback" not in capsys.readouterr().err
+
