Migrate tk backend tests into subprocesses

Try to isolate suspected interactions between tests

Author: richardsheridan

lib/matplotlib/tests/test_backend_tk.py

@@ -1,12 +1,12 @@
 import os
 import subprocess
 import sys
-import tkinter
 
 import numpy as np
 import pytest
 
 from matplotlib import pyplot as plt
+_test_timeout = 10  # Empirically, 1s is not enough on Travis.
 
 
 @pytest.mark.backend('TkAgg', skip_on_importerror=True)
@@ -36,25 +36,42 @@ def evil_blit(photoimage, aggimage, offsets, bboxptr):
 
 @pytest.mark.backend('TkAgg', skip_on_importerror=True)
 def test_figuremanager_preserves_host_mainloop():
-    success = False
-
-    def do_plot():
-        plt.figure()
-        plt.plot([1, 2], [3, 5])
-        plt.close()
-        root.after(0, legitimate_quit)
+    script = """
+import tkinter
+import matplotlib.pyplot as plt
+success = False
 
-    def legitimate_quit():
-        root.quit()
-        nonlocal success
-        success = True
+def do_plot():
+    plt.figure()
+    plt.plot([1, 2], [3, 5])
+    plt.close()
+    root.after(0, legitimate_quit)
 
-    root = tkinter.Tk()
-    root.after(0, do_plot)
-    root.mainloop()
+def legitimate_quit():
+    root.quit()
+    global success
+    success = True
 
-    assert success
+root = tkinter.Tk()
+root.after(0, do_plot)
+root.mainloop()
 
+if success:
+    print("success")
+"""
+    try:
+        proc = subprocess.run(
+            [sys.executable, "-c", script,],
+            env={**os.environ, "SOURCE_DATE_EPOCH": "0"},
+            timeout=_test_timeout,
+            stdout=subprocess.PIPE,
+            check=True,
+            universal_newlines=True,
+        )
+    except subprocess.CalledProcessError:
+        pytest.fail("Subprocess failed to test intended behavior")
+    else:
+        assert proc.stdout.count("success") == 1
 
 @pytest.mark.backend('TkAgg', skip_on_importerror=True)
 @pytest.mark.flaky(reruns=3)
@@ -90,7 +107,7 @@ def target():
             env={**os.environ,
                  "MPLBACKEND": "TkAgg",
                  "SOURCE_DATE_EPOCH": "0"},
-            timeout=10,
+            timeout=_test_timeout,
             stdout=subprocess.PIPE,
             universal_newlines=True,
             check=True
@@ -102,6 +119,52 @@ def target():
     assert proc.stdout.count("success") == 1
 
 
+@pytest.mark.backend('TkAgg', skip_on_importerror=True)
+@pytest.mark.flaky(reruns=3)
+def test_never_update():
+    script = """
+import tkinter
+del tkinter.Misc.update
+del tkinter.Misc.update_idletasks
+
+import matplotlib.pyplot as plt
+fig = plt.figure()
+plt.show(block=False)
+
+# regression test on FigureCanvasTkAgg
+plt.draw()
+# regression test on NavigationToolbar2Tk
+fig.canvas.toolbar.configure_subplots()
+
+# 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)
+"""
+    try:
+        proc = subprocess.run(
+            [sys.executable, "-c", script,],
+            env={**os.environ, "SOURCE_DATE_EPOCH": "0"},
+            timeout=_test_timeout,
+            capture_output=True,
+            check=True,
+            universal_newlines=True,
+        )
+    except subprocess.CalledProcessError:
+        pytest.fail("Subprocess failed to test intended behavior")
+    else:
+        # test framework doesn't see tkinter callback exceptions normally
+        # see tkinter.Misc.report_callback_exception
+        assert "Exception in Tkinter callback" not in proc.stderr
+    finally:
+        # make sure we can see other issues
+        print(proc.stderr, file=sys.stderr)
+
+
 @pytest.mark.backend('TkAgg', skip_on_importerror=True)
 def test_missing_back_button():
     from matplotlib.backends.backend_tkagg import NavigationToolbar2Tk

lib/matplotlib/tests/test_backends_interactive.py

@@ -201,35 +201,6 @@ def test_webagg():
     assert proc.wait(timeout=_test_timeout) == 0
 
 
-@pytest.mark.backend('TkAgg', skip_on_importerror=True)
-def test_never_update(monkeypatch, capsys):
-    import tkinter
-    monkeypatch.delattr(tkinter.Misc, 'update')
-    monkeypatch.delattr(tkinter.Misc, 'update_idletasks')
-
-    import matplotlib.pyplot as plt
-    fig = plt.figure()
-    plt.show(block=False)
-
-    # regression test on FigureCanvasTkAgg
-    plt.draw()
-    # regression test on NavigationToolbar2Tk
-    fig.canvas.toolbar.configure_subplots()
-
-    # 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
-
-
 @pytest.mark.skipif(sys.platform != "linux", reason="this a linux-only test")
 @pytest.mark.backend('Qt5Agg', skip_on_importerror=True)
 def test_lazy_linux_headless():