TST: Catch fork failures and mark them as xfail instead of fail.

Not a pass, but not the fault of the test.

TST,BUG: Move pytest import to just before its use.

Hopefully this fixes the doc builds.

Author: DWesl

lib/matplotlib/testing/__init__.py

@@ -66,16 +66,23 @@ def subprocess_run_helper(func, *args, timeout, extra_env=None):
     """
     target = func.__name__
     module = func.__module__
-    proc = subprocess.run(
-        [sys.executable,
-         "-c",
-         f"from {module} import {target}; {target}()",
-         *args],
-        env={**os.environ, "SOURCE_DATE_EPOCH": "0", **(extra_env or {})},
-        timeout=timeout, check=True,
-        stdout=subprocess.PIPE,
-        stderr=subprocess.PIPE,
-        universal_newlines=True)
+    try:
+        proc = subprocess.run(
+            [sys.executable,
+             "-c",
+             f"from {module} import {target}; {target}()",
+             *args],
+            env={**os.environ, "SOURCE_DATE_EPOCH": "0", **(extra_env or {})},
+            timeout=timeout, check=True,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+            universal_newlines=True)
+    except BlockingIOError:
+        if sys.platform == "cygwin":
+            import pytest
+            pytest.xfail("Fork failure")
+        else:
+            raise
     return proc
 
 

lib/matplotlib/tests/test_sphinxext.py

@@ -27,9 +27,16 @@ def test_tinypages(tmp_path):
     # On CI, gcov emits warnings (due to agg headers being included with the
     # same name in multiple extension modules -- but we don't care about their
     # coverage anyways); hide them using GCOV_ERROR_FILE.
-    proc = Popen(
-        cmd, stdout=PIPE, stderr=PIPE, universal_newlines=True,
-        env={**os.environ, "MPLBACKEND": "", "GCOV_ERROR_FILE": os.devnull})
+    try:
+        proc = Popen(
+            cmd, stdout=PIPE, stderr=PIPE, universal_newlines=True,
+            env={**os.environ, "MPLBACKEND": "", "GCOV_ERROR_FILE": os.devnull}
+        )
+    except BlockingIOError:
+        if sys.platform == "cygwin":
+            pytest.xfail("Fork failure")
+        else:
+            raise
     out, err = proc.communicate()
 
     # Build the pages with warnings turned into errors
@@ -166,8 +173,14 @@ def build_sphinx_html(tmp_path, doctree_dir, html_dir, extra_args=None):
     extra_args = [] if extra_args is None else extra_args
     cmd = [sys.executable, '-msphinx', '-W', '-b', 'html',
            '-d', str(doctree_dir), str(tmp_path), str(html_dir), *extra_args]
-    proc = Popen(cmd, stdout=PIPE, stderr=PIPE, universal_newlines=True,
-                 env={**os.environ, "MPLBACKEND": ""})
+    try:
+        proc = Popen(cmd, stdout=PIPE, stderr=PIPE, universal_newlines=True,
+                     env={**os.environ, "MPLBACKEND": ""})
+    except BlockingIOError:
+        if sys.platform == "cygwin":
+            pytest.xfail("Fork failure")
+        else:
+            raise
     out, err = proc.communicate()
 
     assert proc.returncode == 0, \