universal subprocesses

add note to continue the concept going forward

Author: richardsheridan

lib/matplotlib/tests/test_backend_tk.py

@@ -2,36 +2,61 @@
 import subprocess
 import sys
 
-import numpy as np
 import pytest
 
-from matplotlib import pyplot as plt
 _test_timeout = 10  # Empirically, 1s is not enough on Travis.
 
+# NOTE: TkAgg tests seem to have interactions between tests,
+# So isolate each test in a subprocess. See GH#18261
+
 
 @pytest.mark.backend('TkAgg', skip_on_importerror=True)
 def test_blit():
-    from matplotlib.backends import _tkagg
-    def evil_blit(photoimage, aggimage, offsets, bboxptr):
-        data = np.asarray(aggimage)
-        height, width = data.shape[:2]
-        dataptr = (height, width, data.ctypes.data)
-        _tkagg.blit(
-            photoimage.tk.interpaddr(), str(photoimage), dataptr, offsets,
-            bboxptr)
-
-    fig, ax = plt.subplots()
-    for bad_boxes in ((-1, 2, 0, 2),
-                      (2, 0, 0, 2),
-                      (1, 6, 0, 2),
-                      (0, 2, -1, 2),
-                      (0, 2, 2, 0),
-                      (0, 2, 1, 6)):
-        with pytest.raises(ValueError):
-            evil_blit(fig.canvas._tkphoto,
-                      np.ones((4, 4, 4)),
-                      (0, 1, 2, 3),
-                      bad_boxes)
+    script = """
+import matplotlib.pyplot as plt
+import numpy as np
+from matplotlib.backends import _tkagg
+def evil_blit(photoimage, aggimage, offsets, bboxptr):
+    data = np.asarray(aggimage)
+    height, width = data.shape[:2]
+    dataptr = (height, width, data.ctypes.data)
+    _tkagg.blit(
+        photoimage.tk.interpaddr(), str(photoimage), dataptr, offsets,
+        bboxptr)
+
+fig, ax = plt.subplots()
+bad_boxes = ((-1, 2, 0, 2),
+             (2, 0, 0, 2),
+             (1, 6, 0, 2),
+             (0, 2, -1, 2),
+             (0, 2, 2, 0),
+             (0, 2, 1, 6))
+for bad_box in bad_boxes:
+    try:
+        evil_blit(fig.canvas._tkphoto,
+                  np.ones((4, 4, 4)),
+                  (0, 1, 2, 3),
+                  bad_box)
+    except ValueError:
+        print("success")
+"""
+    try:
+        proc = subprocess.run(
+            [sys.executable, "-c", script],
+            env={**os.environ,
+                 "MPLBACKEND": "TkAgg",
+                 "SOURCE_DATE_EPOCH": "0"},
+            timeout=_test_timeout,
+            stdout=subprocess.PIPE,
+            check=True,
+            universal_newlines=True,
+        )
+    except subprocess.CalledProcessError:
+        pytest.fail("Likely regression on out-of-bounds data access"
+                    " in _tkagg.cpp")
+    else:
+        print(proc.stdout)
+        assert proc.stdout.count("success") == 6  # len(bad_boxes)
 
 
 @pytest.mark.backend('TkAgg', skip_on_importerror=True)
@@ -172,12 +197,32 @@ def test_never_update():
 
 @pytest.mark.backend('TkAgg', skip_on_importerror=True)
 def test_missing_back_button():
-    from matplotlib.backends.backend_tkagg import NavigationToolbar2Tk
-    class Toolbar(NavigationToolbar2Tk):
-        # only display the buttons we need
-        toolitems = [t for t in NavigationToolbar2Tk.toolitems if
-                     t[0] in ('Home', 'Pan', 'Zoom')]
-
-    fig = plt.figure()
-    # this should not raise
-    Toolbar(fig.canvas, fig.canvas.manager.window)
+    script = """
+import matplotlib.pyplot as plt
+from matplotlib.backends.backend_tkagg import NavigationToolbar2Tk
+class Toolbar(NavigationToolbar2Tk):
+    # only display the buttons we need
+    toolitems = [t for t in NavigationToolbar2Tk.toolitems if
+                 t[0] in ('Home', 'Pan', 'Zoom')]
+
+fig = plt.figure()
+print("setup complete")
+# this should not raise
+Toolbar(fig.canvas, fig.canvas.manager.window)
+print("success")
+"""
+    try:
+        proc = subprocess.run(
+            [sys.executable, "-c", script],
+            env={**os.environ,
+                 "MPLBACKEND": "TkAgg",
+                 "SOURCE_DATE_EPOCH": "0"},
+            timeout=_test_timeout,
+            stdout=subprocess.PIPE,
+            universal_newlines=True,
+        )
+    except subprocess.TimeoutExpired:
+        pytest.fail("Subprocess timed out")
+    else:
+        assert proc.stdout.count("setup complete") == 1
+        assert proc.stdout.count("success") == 1