TST: Run test_getattr for backends in a subprocess

For example, GTK3 and GTK4 conflict, and which one is tested depends on
which one loads first. Running in a subprocess ensures that both work,
but we only do that for backends as adding ~100 more subprocesses is
overkill.

Author: QuLogic

lib/matplotlib/tests/test_getattr.py

@@ -1,25 +1,29 @@
 from importlib import import_module
 from pkgutil import walk_packages
+import sys
+import warnings
 
-import matplotlib
 import pytest
 
+import matplotlib
+from matplotlib.testing import is_ci_environment, subprocess_run_helper
+
 # Get the names of all matplotlib submodules,
 # except for the unit tests and private modules.
-module_names = [
-    m.name
-    for m in walk_packages(
-        path=matplotlib.__path__, prefix=f'{matplotlib.__name__}.'
-    )
-    if not m.name.startswith(__package__)
-    and not any(x.startswith('_') for x in m.name.split('.'))
-]
+module_names = []
+backend_module_names = []
+for m in walk_packages(path=matplotlib.__path__, prefix=f'{matplotlib.__name__}.'):
+    if m.name.startswith(__package__):
+        continue
+    if any(x.startswith('_') for x in m.name.split('.')):
+        continue
+    if 'backends.backend_' in m.name:
+        backend_module_names.append(m.name)
+    else:
+        module_names.append(m.name)
 
 
-@pytest.mark.parametrize('module_name', module_names)
-@pytest.mark.filterwarnings('ignore::DeprecationWarning')
-@pytest.mark.filterwarnings('ignore::ImportWarning')
-def test_getattr(module_name):
+def _test_getattr(module_name, use_pytest=True):
     """
     Test that __getattr__ methods raise AttributeError for unknown keys.
     See #20822, #20855.
@@ -28,8 +32,35 @@ def test_getattr(module_name):
         module = import_module(module_name)
     except (ImportError, RuntimeError, OSError) as e:
         # Skip modules that cannot be imported due to missing dependencies
-        pytest.skip(f'Cannot import {module_name} due to {e}')
+        if use_pytest:
+            pytest.skip(f'Cannot import {module_name} due to {e}')
+        else:
+            print(f'SKIP: Cannot import {module_name} due to {e}')
+            return
 
     key = 'THIS_SYMBOL_SHOULD_NOT_EXIST'
     if hasattr(module, key):
         delattr(module, key)
+
+
+@pytest.mark.parametrize('module_name', module_names)
+@pytest.mark.filterwarnings('ignore::DeprecationWarning')
+@pytest.mark.filterwarnings('ignore::ImportWarning')
+def test_getattr(module_name):
+    _test_getattr(module_name)
+
+
+def _test_module_getattr():
+    warnings.filterwarnings('ignore', category=DeprecationWarning)
+    warnings.filterwarnings('ignore', category=ImportWarning)
+    module_name = sys.argv[1]
+    _test_getattr(module_name, use_pytest=False)
+
+
+@pytest.mark.parametrize('module_name', backend_module_names)
+def test_backend_getattr(module_name):
+    proc = subprocess_run_helper(_test_module_getattr, module_name,
+                                 timeout=120 if is_ci_environment() else 20)
+    if 'SKIP: ' in proc.stdout:
+        pytest.skip(proc.stdout.removeprefix('SKIP: '))
+    print(proc.stdout)