chore: add missing nox sessions and polish dependencies in sqlalchemy-spanner (googleapis#17285)

## Description
This PR implements missing nox sessions and refactors dependency
management inside `packages/sqlalchemy-spanner/noxfile.py` to align with
google-cloud standard practices.

---

## Key Changes

### 1. Constants Architecture
All dependencies and version definitions have been concentrated at the
top of `noxfile.py` in nestled constants:
* `UNIT_TEST_STANDARD_DEPENDENCIES`: Standard testing frameworks
(`mock`, `pytest`).
* `UNIT_TEST_EXTERNAL_DEPENDENCIES`: Telemetry requirements (fully
unpinned: `setuptools`, `opentelemetry-api`, `opentelemetry-sdk`,
`opentelemetry-instrumentation` to delegate version resolution strictly
to `setup.py` and `constraints`).
* `UNIT_TEST_DEPENDENCIES`: SQLAlchemy version specifications under test
(`sqlalchemy>=2.0`).

### 2. Expired database management
Updated the `create_test_database.py` file to add or tweak code to
ensure that expired databases are quickly deleted. During rapid
development cycles, the Spanner database count would quickly reach the
Spanner limit of 100 and system tests would fail. There were two
conditions that contributed being unable to quickly retest. In some
cases the system would not delete old databases at all because certain
triggers were not created. And in other cases, you needed to wait 4
hours before the databases would age off and you could run the system
tests again.

### NOTES:
* **`core_deps_from_source` & `prerelease_deps`**: Target packages are
cleanly overwritten with local source paths/pre-releases using pip's
native `--ignore-installed --no-deps` flags.
* **`mypy` & `docs` & `docfx`**: Configured to skip gracefully with
standard todos indicating that typehints and docs folders are not
present in this package.
* **`cover`**: Added standard coverage session which skips gracefully if
no `.coverage` database file has been created yet.
* **`format`**: Implemented Ruff format and check sessions, and
reformatted imports and code to team standards.

Fixes googleapis#17048 🦖

Author: chalmerlowe

packages/sqlalchemy-spanner/create_test_database.py

@@ -15,6 +15,7 @@
 # limitations under the License.
 
 import os
+import re
 import time
 
 from google.api_core import datetime_helpers
@@ -68,19 +69,30 @@ def delete_stale_test_instances():
 
 
 def delete_stale_test_databases():
-    """Delete test databases that are older than four hours."""
-    cutoff = (int(time.time()) - 4 * 60 * 60) * 1000
+    """Delete test databases that are older than 10 minutes.
+    
+    In this test suite, active databases typically finish running in ~5 minutes.
+    To prevent concurrent Kokoro runs from accidentally deleting each other's
+    active databases we use a 10-minute safety threshold. Without an aggressive
+    cutoff we quickly bump up against Cloud Spanner's limit of 100 databases per instance.
+    """
+    cutoff = (int(time.time()) - 10 * 60) * 1000
     instance = CLIENT.instance("sqlalchemy-dialect-test")
     if not instance.exists():
         return
     database_pbs = instance.list_databases()
     for database_pb in database_pbs:
         database = Database.from_pb(database_pb, instance)
-        # The emulator does not return a create_time for databases.
-        if database.create_time is None:
-            continue
-        create_time = datetime_helpers.to_milliseconds(database_pb.create_time)
-        if create_time > cutoff:
+        # Parse creation time from database ID first (e.g. "sqlalchemy-test-1779989493809")
+        # to be 100% independent of emulator metadata or GCP Client API create_time gaps!
+        create_time = None
+        match = re.match(r"sqlalchemy-test-(\d+)", database.database_id)
+        if match:
+            create_time = int(match.group(1))
+        elif database_pb.create_time is not None:
+            create_time = datetime_helpers.to_milliseconds(database_pb.create_time)
+
+        if create_time is None or create_time > cutoff:
             continue
         try:
             database.drop()

packages/sqlalchemy-spanner/google/cloud/sqlalchemy_spanner/__init__.py

@@ -13,8 +13,6 @@
 # limitations under the License.
 
 from .sqlalchemy_spanner import SpannerDialect
-
 from .version import __version__
 
-
 __all__ = (SpannerDialect, __version__)

packages/sqlalchemy-spanner/google/cloud/sqlalchemy_spanner/_opentelemetry_tracing.py

@@ -16,7 +16,6 @@
 
 import collections
 import os
-
 from contextlib import contextmanager
 
 from google.api_core.exceptions import GoogleAPICallError

packages/sqlalchemy-spanner/google/cloud/sqlalchemy_spanner/requirements.py

@@ -13,8 +13,8 @@
 # limitations under the License.
 
 from sqlalchemy.testing import exclusions
-from sqlalchemy.testing.requirements import SuiteRequirements
 from sqlalchemy.testing.exclusions import against, only_on
+from sqlalchemy.testing.requirements import SuiteRequirements
 
 
 class Requirements(SuiteRequirements):  # pragma: no cover

packages/sqlalchemy-spanner/google/cloud/sqlalchemy_spanner/sqlalchemy_spanner.py

@@ -12,9 +12,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import base64
-
 import re
 
+import sqlalchemy
 from alembic.ddl.base import (
     ColumnNullable,
     ColumnType,
@@ -26,32 +26,30 @@
 from google.api_core.client_options import ClientOptions
 from google.auth.credentials import AnonymousCredentials
 from google.cloud.spanner_v1 import Client, TransactionOptions
-from sqlalchemy.exc import NoSuchTableError
-from sqlalchemy.sql import elements
-from sqlalchemy import ForeignKeyConstraint, types, TypeDecorator, PickleType
+from google.cloud.spanner_v1.data_types import JsonObject
+from sqlalchemy import ForeignKeyConstraint, PickleType, TypeDecorator, types
 from sqlalchemy.engine.base import Engine
 from sqlalchemy.engine.default import DefaultDialect, DefaultExecutionContext
 from sqlalchemy.event import listens_for
+from sqlalchemy.exc import NoSuchTableError
 from sqlalchemy.ext.compiler import compiles
 from sqlalchemy.pool import Pool
+from sqlalchemy.sql import elements, expression
 from sqlalchemy.sql.compiler import (
-    selectable,
+    OPERATORS,
+    RESERVED_WORDS,
     DDLCompiler,
     GenericTypeCompiler,
     IdentifierPreparer,
     SQLCompiler,
-    OPERATORS,
-    RESERVED_WORDS,
+    selectable,
 )
 from sqlalchemy.sql.default_comparator import operator_lookup
 from sqlalchemy.sql.operators import json_getitem_op
-from sqlalchemy.sql import expression
 
-from google.cloud.spanner_v1.data_types import JsonObject
 from google.cloud import spanner_dbapi
-from google.cloud.sqlalchemy_spanner._opentelemetry_tracing import trace_call
 from google.cloud.sqlalchemy_spanner import version as sqlalchemy_spanner_version
-import sqlalchemy
+from google.cloud.sqlalchemy_spanner._opentelemetry_tracing import trace_call
 
 USING_SQLACLCHEMY_20 = False
 if sqlalchemy.__version__.split(".")[0] == "2":
@@ -223,9 +221,9 @@ def pre_exec(self):
         if ignore_transaction_warnings is not None:
             conn = self._dbapi_connection.connection
             if conn is not None and hasattr(conn, "_connection_variables"):
-                conn._connection_variables[
-                    "ignore_transaction_warnings"
-                ] = ignore_transaction_warnings
+                conn._connection_variables["ignore_transaction_warnings"] = (
+                    ignore_transaction_warnings
+                )
 
     def fire_sequence(self, seq, type_):
         """Builds a statement for fetching next value of the sequence."""
@@ -416,7 +414,7 @@ def limit_clause(self, select, **kw):
             text += "\n LIMIT " + self.process(select._limit_clause, **kw)
         if select._offset_clause is not None:
             if select._limit_clause is None:
-                text += f"\n LIMIT {9223372036854775807-select._offset}"
+                text += f"\n LIMIT {9223372036854775807 - select._offset}"
             text += " OFFSET " + self.process(select._offset_clause, **kw)
         return text
 
@@ -1025,9 +1023,7 @@ def get_view_names(self, connection, schema=None, **kw):
             SELECT table_name
             FROM information_schema.views
             WHERE TABLE_SCHEMA='{}'
-            """.format(
-            schema or ""
-        )
+            """.format(schema or "")
 
         all_views = []
         with connection.connection.database.snapshot() as snap:
@@ -1056,9 +1052,7 @@ def get_sequence_names(self, connection, schema=None, **kw):
             SELECT name
             FROM information_schema.sequences
             WHERE SCHEMA='{}'
-            """.format(
-            schema or ""
-        )
+            """.format(schema or "")
         all_sequences = []
         with connection.connection.database.snapshot() as snap:
             rows = list(snap.execute_sql(sql))
@@ -1087,9 +1081,7 @@ def get_view_definition(self, connection, view_name, schema=None, **kw):
             SELECT view_definition
             FROM information_schema.views
             WHERE TABLE_SCHEMA='{schema_name}' AND TABLE_NAME='{view_name}'
-            """.format(
-            schema_name=schema or "", view_name=view_name
-        )
+            """.format(schema_name=schema or "", view_name=view_name)
 
         with connection.connection.database.snapshot() as snap:
             rows = list(snap.execute_sql(sql))
@@ -1623,9 +1615,7 @@ def get_table_names(self, connection, schema=None, **kw):
 SELECT table_name
 FROM information_schema.tables
 WHERE table_type = 'BASE TABLE' AND table_schema = '{schema}'
-""".format(
-            schema=schema or ""
-        )
+""".format(schema=schema or "")
 
         table_names = []
         with connection.connection.database.snapshot() as snap:
@@ -1661,9 +1651,7 @@ def get_unique_constraints(self, connection, table_name, schema=None, **kw):
     AND tc.TABLE_SCHEMA="{table_schema}"
     AND tc.CONSTRAINT_TYPE = "UNIQUE"
     AND tc.CONSTRAINT_NAME IS NOT NULL
-""".format(
-            table_schema=schema or "", table_name=table_name
-        )
+""".format(table_schema=schema or "", table_name=table_name)
 
         cols = []
         with connection.connection.database.snapshot() as snap:
@@ -1696,9 +1684,7 @@ def has_table(self, connection, table_name, schema=None, **kw):
 FROM INFORMATION_SCHEMA.TABLES
 WHERE TABLE_SCHEMA="{table_schema}" AND TABLE_NAME="{table_name}"
 LIMIT 1
-""".format(
-                    table_schema=schema or "", table_name=table_name
-                )
+""".format(table_schema=schema or "", table_name=table_name)
             )
 
             for _ in rows:
@@ -1723,9 +1709,7 @@ def has_sequence(self, connection, sequence_name, schema=None, **kw):
                 WHERE NAME="{sequence_name}"
                 AND SCHEMA="{schema}"
                 LIMIT 1
-                """.format(
-                    sequence_name=sequence_name, schema=schema or ""
-                )
+                """.format(sequence_name=sequence_name, schema=schema or "")
             )
 
             for _ in rows: