run pytester subprocess when matplotlib built with pybind11 v3

Author: ConorMacBride

tests/conftest.py

@@ -7,3 +7,12 @@
     @pytest.fixture
     def pytester(testdir):
         return testdir
+
+
+def pytest_configure(config):
+    # Matplotlib versions build with pybind11 3.0.0 or later
+    # encounter import issues unless run in subprocess mode.
+    # See: https://github.com/matplotlib/pytest-mpl/issues/248
+    import matplotlib
+    if Version(matplotlib.__version__) > Version("3.10.3"):
+        config.option.runpytest = "subprocess"