QA: Add EOL/deprecation warning about support for SQLAlchemy 1.3

src/crate/client/sqlalchemy/__init__.py

@@ -23,10 +23,24 @@
 from .dialect import CrateDialect
 from .sa_version import SA_1_4, SA_VERSION
 
-# SQLAlchemy 1.3 does not have the `exec_driver_sql` method.
+
 if SA_VERSION < SA_1_4:
+    import textwrap
+    import warnings
+
+    # SQLAlchemy 1.3 is effectively EOL.
+    SA13_DEPRECATION_WARNING = textwrap.dedent("""
+    WARNING: SQLAlchemy 1.3 is effectively EOL.
+    With SQLAlchemy 2 around the corner, this will be even more immanent.
+    Future versions of the CrateDB SQLAlchemy dialect will drop support for SQLAlchemy 1.3.
+    It is recommended that you transition to using SQLAlchemy 1.4 or 2.0.
+    """.lstrip("\n"))
+    warnings.warn(message=SA13_DEPRECATION_WARNING, category=DeprecationWarning)
+
+    # SQLAlchemy 1.3 does not have the `exec_driver_sql` method, so add it.
     monkeypatch_add_exec_driver_sql()
 
+
 __all__ = [
     CrateDialect,
 ]

src/crate/client/sqlalchemy/tests/__init__.py

@@ -21,6 +21,7 @@
 from .array_test import SqlAlchemyArrayTypeTest
 from .dialect_test import SqlAlchemyDialectTest
 from .function_test import SqlAlchemyFunctionTest
+from .warnings_test import SqlAlchemyWarningsTest
 
 
 def test_suite():
@@ -38,4 +39,5 @@ def test_suite():
     tests.addTest(makeSuite(SqlAlchemyDialectTest))
     tests.addTest(makeSuite(SqlAlchemyFunctionTest))
     tests.addTest(makeSuite(SqlAlchemyArrayTypeTest))
+    tests.addTest(makeSuite(SqlAlchemyWarningsTest))
     return tests

src/crate/client/sqlalchemy/tests/warnings_test.py

@@ -0,0 +1,30 @@
+# -*- coding: utf-8; -*-
+import sys
+import warnings
+from unittest import TestCase
+
+from crate.testing.util import ExtraAssertions
+
+
+class SqlAlchemyWarningsTest(TestCase, ExtraAssertions):
+
+    def test_sa13_deprecation_warning(self):
+        """
+        Verify that a `DeprecationWarning` is issued when running SQLAlchemy 1.3.
+
+        https://docs.python.org/3/library/warnings.html#testing-warnings
+        """
+        with warnings.catch_warnings(record=True) as w:
+
+            # Cause all warnings to always be triggered.
+            warnings.simplefilter("always")
+
+            # Trigger a warning by importing the SQLAlchemy dialect module.
+            # Because it already has been loaded, unload it beforehand.
+            del sys.modules["crate.client.sqlalchemy"]
+            import crate.client.sqlalchemy  # noqa: F401
+
+            # Verify details of the SA13 EOL/deprecation warning.
+            self.assertEqual(len(w), 1)
+            self.assertIsSubclass(w[-1].category, DeprecationWarning)
+            self.assertIn("SQLAlchemy 1.3 is effectively EOL.", str(w[-1].message))

src/crate/testing/util.py

@@ -0,0 +1,20 @@
+class ExtraAssertions:
+    """
+    Additional assert methods for unittest.
+
+    - https://github.com/python/cpython/issues/71339
+    - https://bugs.python.org/issue14819
+    - https://bugs.python.org/file43047/extra_assertions.patch
+    """
+
+    def assertIsSubclass(self, cls, superclass, msg=None):
+        try:
+            r = issubclass(cls, superclass)
+        except TypeError:
+            if not isinstance(cls, type):
+                self.fail(self._formatMessage(msg,
+                          '%r is not a class' % (cls,)))
+            raise
+        if not r:
+            self.fail(self._formatMessage(msg,
+                      '%r is not a subclass of %r' % (cls, superclass)))