comment stub and filename change (#2453)

Co-authored-by: Garth N. Wells <gnw20@cam.ac.uk>

python/test/unit/common/test_python_implemented.py → python/test/unit/common/test_public_api.py

@@ -21,6 +21,11 @@ def collect_pkg_modules_recursive(name):
 
 
 def test_all_implemented():
+    """
+    flake8 does not catch its warning code F822: whether the public API
+    offered by the members of __all__ are implemented. We therefore manually
+    check.
+    """
     module_names = collect_pkg_modules_recursive("dolfinx")
     for module_name in module_names:
         module = importlib.import_module(module_name)