DEPR/REGR: Fix pandas.util.testing deprecation

pandas/tests/api/test_api.py

@@ -1,3 +1,4 @@
+import sys
 from typing import List
 
 import pandas as pd
@@ -288,14 +289,20 @@ def test_testing(self):
         self.check(testing, self.funcs)
 
     def test_util_testing_deprecated(self):
-        s = pd.Series([], dtype="object")
-        with tm.assert_produces_warning(FutureWarning) as m:
-            import pandas.util.testing as tm2
+        # avoid cache state affecting the test
+        sys.modules.pop("pandas.util.testing", None)
 
-            tm2.assert_series_equal(s, s)
+        with tm.assert_produces_warning(FutureWarning) as m:
+            import pandas.util.testing  # noqa: F401
 
-        assert "pandas.testing.assert_series_equal" in str(m[0].message)
+        assert "pandas.util.testing is deprecated" in str(m[0].message)
+        assert "pandas.testing instead" in str(m[0].message)
 
+    def test_util_testing_deprecated_direct(self):
+        # avoid cache state affecting the test
+        sys.modules.pop("pandas.util.testing", None)
         with tm.assert_produces_warning(FutureWarning) as m:
-            tm2.DataFrame
-        assert "removed" in str(m[0].message)
+            from pandas.util.testing import assert_series_equal  # noqa: F401
+
+        assert "pandas.util.testing is deprecated" in str(m[0].message)
+        assert "pandas.testing instead" in str(m[0].message)

pandas/util/__init__.py

@@ -1,4 +1,60 @@
-from pandas.util._decorators import Appender, Substitution, cache_readonly  # noqa
+import importlib as _importlib
+from importlib.abc import Loader as _Loader, MetaPathFinder
+from importlib.machinery import ModuleSpec as _ModuleSpec
+import sys as _sys
+import warnings as _warnings
 
-from pandas.core.util.hashing import hash_array, hash_pandas_object  # noqa
-from pandas.util.testing import testing  # noqa: F401
+from pandas.util._decorators import Appender, Substitution, cache_readonly
+
+from pandas.core.util.hashing import hash_array, hash_pandas_object
+
+# Custom import hook for the deprecated pandas.util.testing module.
+# The custom Finder only runs when python's standard import fail,
+# since we're adding to the end of sys.meta_path. In TestingLoader.create_module
+# we simply warn and then return the real testing module, pandas._testing.
+# This differs from _DeprecatedModule by using the import system, which
+# allows it to work with both `import foo; foo.bar` and `from foo import bar`.
+# But because Python caches imports, the warning appears only once.
+
+
+class _TestingFinder(MetaPathFinder):
+    @classmethod
+    def find_spec(cls, fullname, path=None, target=None):
+
+        name_parts = fullname.split(".")
+        if name_parts[:3] != ["pandas", "util", "testing"] or len(name_parts) > 3:
+            return None
+        else:
+            # return ModuleSpec(fullname, DataPackageImporter())
+            return _ModuleSpec(fullname, _TestingLoader())
+
+
+class _TestingLoader(_Loader):
+    @classmethod
+    def create_module(cls, spec):
+        module = _importlib.import_module("pandas._testing")
+        _warnings.warn(
+            (
+                "pandas.util.testing is deprecated. Use the "
+                "public methods from pandas.testing instead."
+            ),
+            FutureWarning,
+            stacklevel=2,
+        )
+        return module
+
+    @classmethod
+    def exec_module(cls, module):
+        pass
+
+
+_sys.meta_path.append(_TestingFinder())
+
+
+__all__ = [
+    "Appender",
+    "Substitution",
+    "cache_readonly",
+    "hash_array",
+    "hash_pandas_object",
+]