reinvent xdist hooks in terms of pytest fixtures

To allow the "connection" pytest fixture and others work
correctly in conjunction with setup/teardown that expects
to be external to the transaction, remove and prevent any usage
of "xdist" style names that are hardcoded by pytest to run
inside of fixtures, even function level ones.   Instead use
pytest autouse fixtures to implement our own
r"setup|teardown_test(?:_class)?" methods so that we can ensure
function-scoped fixtures are run within them.   A new more
explicit flow is set up within plugin_base and pytestplugin
such that the order of setup/teardown steps, which there are now
many, is fully documented and controllable.   New granularity
has been added to the test teardown phase to distinguish
between "end of the test" when lock-holding structures on
connections should be released to allow for table drops,
vs. "end of the test plus its teardown steps" when we can
perform final cleanup on connections and run assertions
that everything is closed out.

From there we can remove most of the defensive "tear down everything"
logic inside of engines which for many years would frequently dispose
of pools over and over again, creating for a broken and expensive
connection flow.  A quick test shows that running test/sql/ against
a single Postgresql engine with the new approach uses 75% fewer new
connections, creating 42 new connections total, vs. 164 new
connections total with the previous system.

As part of this, the new fixtures metadata/connection/future_connection
have been integrated such that they can be combined together
effectively.  The fixture_session(), provide_metadata() fixtures
have been improved, including that fixture_session() now strongly
references sessions which are explicitly torn down before
table drops occur afer a test.

Major changes have been made to the
ConnectionKiller such that it now features different "scopes" for
testing engines and will limit its cleanup to those testing
engines corresponding to end of test, end of test class, or
end of test session.   The system by which it tracks DBAPI
connections has been reworked, is ultimately somewhat similar to
how it worked before but is organized more clearly along
with the proxy-tracking logic.  A "testing_engine" fixture
is also added that works as a pytest fixture rather than a
standalone function.  The connection cleanup logic should
now be very robust, as we now can use the same global
connection pools for the whole suite without ever disposing
them, while also running a query for PostgreSQL
locks remaining after every test and assert there are no open
transactions leaking between tests at all.  Additional steps
are added that also accommodate for asyncio connections not
explicitly closed, as is the case for legacy sync-style
tests as well as the async tests themselves.

As always, hundreds of tests are further refined to use the
new fixtures where problems with loose connections were identified,
largely as a result of the new PostgreSQL assertions,
many more tests have moved from legacy patterns into the newest.

An unfortunate discovery during the creation of this system is that
autouse fixtures (as well as if they are set up by
@pytest.mark.usefixtures) are not usable at our current scale with pytest
4.6.11 running under Python 2.  It's unclear if this is due
to the older version of pytest or how it implements itself for
Python 2, as well as if the issue is CPU slowness or just large
memory use, but collecting the full span of tests takes over
a minute for a single process when any autouse fixtures are in
place and on CI the jobs just time out after ten minutes.
So at the moment this patch also reinvents a small version of
"autouse" fixtures when py2k is running, which skips generating
the real fixture and instead uses two global pytest fixtures
(which don't seem to impact performance) to invoke the
"autouse" fixtures ourselves outside of pytest.
This will limit our ability to do more with fixtures
until we can remove py2k support.

py.test is still observed to be much slower in collection in the
4.6.11 version compared to modern 6.2 versions, so add support for new
TOX_POSTGRESQL_PY2K and TOX_MYSQL_PY2K environment variables that
will run the suite for fewer backends under Python 2.  For Python 3
pin pytest to modern 6.2 versions where performance for collection
has been improved greatly.

Includes the following improvements:

Fixed bug in asyncio connection pool where ``asyncio.TimeoutError`` would
be raised rather than :class:`.exc.TimeoutError`.  Also repaired the
:paramref:`_sa.create_engine.pool_timeout` parameter set to zero when using
the async engine, which previously would ignore the timeout and block
rather than timing out immediately as is the behavior with regular
:class:`.QueuePool`.

For asyncio the connection pool will now also not interact
at all with an asyncio connection whose ConnectionFairy is
being garbage collected; a warning that the connection was
not properly closed is emitted and the connection is discarded.
Within the test suite the ConnectionKiller is now maintaining
strong references to all DBAPI connections and ensuring they
are released when tests end, including those whose ConnectionFairy
proxies are GCed.

Identified cx_Oracle.stmtcachesize as a major factor in Oracle
test scalability issues, this can be reset on a per-test basis
rather than setting it to zero across the board.  the addition
of this flag has resolved the long-standing oracle "two task"
error problem.

For SQL Server, changed the temp table style used by the
"suite" tests to be the double-pound-sign, i.e. global,
variety, which is much easier to test generically.  There
are already reflection tests that are more finely tuned
to both styles of temp table within the mssql test
suite.  Additionally, added an extra step to the
"dropfirst" mechanism for SQL Server that will remove
all foreign key constraints first as some issues were
observed when using this flag when multiple schemas
had not been torn down.

Identified and fixed two subtle failure modes in the
engine, when commit/rollback fails in a begin()
context manager, the connection is explicitly closed,
and when "initialize()" fails on the first new connection
of a dialect, the transactional state on that connection
is still rolled back.

Fixes: #5826
Fixes: #5827
Change-Id: Ib1d05cb8c7cf84f9a4bfd23df397dc23c9329bfe

4 files changed, 298 insertions, 46 deletions

diff --git a/lib/sqlalchemy/testing/plugin/bootstrap.py b/lib/sqlalchemy/testing/plugin/bootstrap.py
index a95c947e2..1f568dfc8 100644
--- a/lib/sqlalchemy/testing/plugin/bootstrap.py
+++ b/lib/sqlalchemy/testing/plugin/bootstrap.py
@@ -40,6 +40,11 @@ def load_file_as_module(name):
 
 if to_bootstrap == "pytest":
     sys.modules["sqla_plugin_base"] = load_file_as_module("plugin_base")
+    sys.modules["sqla_plugin_base"].bootstrapped_as_sqlalchemy = True
+    if sys.version_info < (3, 0):
+        sys.modules["sqla_reinvent_fixtures"] = load_file_as_module(
+            "reinvent_fixtures_py2k"
+        )
     sys.modules["sqla_pytestplugin"] = load_file_as_module("pytestplugin")
 else:
     raise Exception("unknown bootstrap: %s" % to_bootstrap)  # noqa
diff --git a/lib/sqlalchemy/testing/plugin/plugin_base.py b/lib/sqlalchemy/testing/plugin/plugin_base.py
index 3594cd276..7851fbb3e 100644
--- a/lib/sqlalchemy/testing/plugin/plugin_base.py
+++ b/lib/sqlalchemy/testing/plugin/plugin_base.py
@@ -21,6 +21,9 @@ import logging
 import re
 import sys
 
+# flag which indicates we are in the SQLAlchemy testing suite,
+# and not that of Alembic or a third party dialect.
+bootstrapped_as_sqlalchemy = False
 
 log = logging.getLogger("sqlalchemy.testing.plugin_base")
 
@@ -381,7 +384,7 @@ def _init_symbols(options, file_config):
 
 @post
 def _set_disable_asyncio(opt, file_config):
-    if opt.disable_asyncio:
+    if opt.disable_asyncio or not py3k:
         from sqlalchemy.testing import asyncio
 
         asyncio.ENABLE_ASYNCIO = False
@@ -458,6 +461,8 @@ def _setup_requirements(argument):
 
     config.requirements = testing.requires = req_cls()
 
+    config.bootstrapped_as_sqlalchemy = bootstrapped_as_sqlalchemy
+
 
 @post
 def _prep_testing_database(options, file_config):
@@ -566,17 +571,22 @@ def generate_sub_tests(cls, module):
         yield cls
 
 
-def start_test_class(cls):
+def start_test_class_outside_fixtures(cls):
     _do_skips(cls)
     _setup_engine(cls)
 
 
 def stop_test_class(cls):
-    # from sqlalchemy import inspect
-    # assert not inspect(testing.db).get_table_names()
+    # close sessions, immediate connections, etc.
+    fixtures.stop_test_class_inside_fixtures(cls)
+
+    # close outstanding connection pool connections, dispose of
+    # additional engines
+    engines.testing_reaper.stop_test_class_inside_fixtures()
 
-    provision.stop_test_class(config, config.db, cls)
-    engines.testing_reaper._stop_test_ctx()
+
+def stop_test_class_outside_fixtures(cls):
+    provision.stop_test_class_outside_fixtures(config, config.db, cls)
     try:
         if not options.low_connections:
             assertions.global_cleanup_assertions()
@@ -590,14 +600,16 @@ def _restore_engine():
 
 
 def final_process_cleanup():
-    engines.testing_reaper._stop_test_ctx_aggressive()
+    engines.testing_reaper.final_cleanup()
     assertions.global_cleanup_assertions()
     _restore_engine()
 
 
 def _setup_engine(cls):
     if getattr(cls, "__engine_options__", None):
-        eng = engines.testing_engine(options=cls.__engine_options__)
+        opts = dict(cls.__engine_options__)
+        opts["scope"] = "class"
+        eng = engines.testing_engine(options=opts)
         config._current.push_engine(eng, testing)
 
 
@@ -614,7 +626,12 @@ def before_test(test, test_module_name, test_class, test_name):
 
 
 def after_test(test):
-    engines.testing_reaper._after_test_ctx()
+    fixtures.after_test()
+    engines.testing_reaper.after_test()
+
+
+def after_test_fixtures(test):
+    engines.testing_reaper.after_test_outside_fixtures(test)
 
 
 def _possible_configs_for_cls(cls, reasons=None, sparse=False):
@@ -748,6 +765,10 @@ class FixtureFunctions(ABC):
     def get_current_test_name(self):
         raise NotImplementedError()
 
+    @abc.abstractmethod
+    def mark_base_test_class(self):
+        raise NotImplementedError()
+
 
 _fixture_fn_class = None
 
diff --git a/lib/sqlalchemy/testing/plugin/pytestplugin.py b/lib/sqlalchemy/testing/plugin/pytestplugin.py
index 46468a07d..4eaaecebb 100644
--- a/lib/sqlalchemy/testing/plugin/pytestplugin.py
+++ b/lib/sqlalchemy/testing/plugin/pytestplugin.py
@@ -17,6 +17,7 @@ import sys
 
 import pytest
 
+
 try:
     import typing
 except ImportError:
@@ -33,6 +34,14 @@ except ImportError:
     has_xdist = False
 
 
+py2k = sys.version_info < (3, 0)
+if py2k:
+    try:
+        import sqla_reinvent_fixtures as reinvent_fixtures_py2k
+    except ImportError:
+        from . import reinvent_fixtures_py2k
+
+
 def pytest_addoption(parser):
     group = parser.getgroup("sqlalchemy")
 
@@ -238,6 +247,10 @@ def pytest_collection_modifyitems(session, config, items):
         else:
             newitems.append(item)
 
+    if py2k:
+        for item in newitems:
+            reinvent_fixtures_py2k.scan_for_fixtures_to_use_for_class(item)
+
     # seems like the functions attached to a test class aren't sorted already?
     # is that true and why's that? (when using unittest, they're sorted)
     items[:] = sorted(
@@ -251,7 +264,6 @@ def pytest_collection_modifyitems(session, config, items):
 
 
 def pytest_pycollect_makeitem(collector, name, obj):
-
     if inspect.isclass(obj) and plugin_base.want_class(name, obj):
         from sqlalchemy.testing import config
 
@@ -259,7 +271,6 @@ def pytest_pycollect_makeitem(collector, name, obj):
             obj = _apply_maybe_async(obj)
 
         ctor = getattr(pytest.Class, "from_parent", pytest.Class)
-
         return [
             ctor(name=parametrize_cls.__name__, parent=collector)
             for parametrize_cls in _parametrize_cls(collector.module, obj)
@@ -287,12 +298,11 @@ def _is_wrapped_coroutine_function(fn):
 def _apply_maybe_async(obj, recurse=True):
     from sqlalchemy.testing import asyncio
 
-    setup_names = {"setup", "setup_class", "teardown", "teardown_class"}
     for name, value in vars(obj).items():
         if (
             (callable(value) or isinstance(value, classmethod))
             and not getattr(value, "_maybe_async_applied", False)
-            and (name.startswith("test_") or name in setup_names)
+            and (name.startswith("test_"))
             and not _is_wrapped_coroutine_function(value)
         ):
             is_classmethod = False
@@ -317,9 +327,6 @@ def _apply_maybe_async(obj, recurse=True):
     return obj
 
 
-_current_class = None
-
-
 def _parametrize_cls(module, cls):
     """implement a class-based version of pytest parametrize."""
 
@@ -355,63 +362,153 @@ def _parametrize_cls(module, cls):
     return classes
 
 
+_current_class = None
+
+
 def pytest_runtest_setup(item):
     from sqlalchemy.testing import asyncio
 
-    # here we seem to get called only based on what we collected
-    # in pytest_collection_modifyitems.   So to do class-based stuff
-    # we have to tear that out.
-    global _current_class
-
     if not isinstance(item, pytest.Function):
         return
 
-    # ... so we're doing a little dance here to figure it out...
+    # pytest_runtest_setup runs *before* pytest fixtures with scope="class".
+    # plugin_base.start_test_class_outside_fixtures may opt to raise SkipTest
+    # for the whole class and has to run things that are across all current
+    # databases, so we run this outside of the pytest fixture system altogether
+    # and ensure asyncio greenlet if any engines are async
+
+    global _current_class
+
     if _current_class is None:
-        asyncio._maybe_async(class_setup, item.parent.parent)
+        asyncio._maybe_async_provisioning(
+            plugin_base.start_test_class_outside_fixtures,
+            item.parent.parent.cls,
+        )
         _current_class = item.parent.parent
 
-        # this is needed for the class-level, to ensure that the
-        # teardown runs after the class is completed with its own
-        # class-level teardown...
         def finalize():
             global _current_class
-            asyncio._maybe_async(class_teardown, item.parent.parent)
             _current_class = None
 
+            asyncio._maybe_async_provisioning(
+                plugin_base.stop_test_class_outside_fixtures,
+                item.parent.parent.cls,
+            )
+
         item.parent.parent.addfinalizer(finalize)
 
-    asyncio._maybe_async(test_setup, item)
 
+def pytest_runtest_call(item):
+    # runs inside of pytest function fixture scope
+    # before test function runs
 
-def pytest_runtest_teardown(item):
     from sqlalchemy.testing import asyncio
 
-    # ...but this works better as the hook here rather than
-    # using a finalizer, as the finalizer seems to get in the way
-    # of the test reporting failures correctly (you get a bunch of
-    # pytest assertion stuff instead)
-    asyncio._maybe_async(test_teardown, item)
+    asyncio._maybe_async(
+        plugin_base.before_test,
+        item,
+        item.parent.module.__name__,
+        item.parent.cls,
+        item.name,
+    )
 
 
-def test_setup(item):
-    plugin_base.before_test(
-        item, item.parent.module.__name__, item.parent.cls, item.name
-    )
+def pytest_runtest_teardown(item, nextitem):
+    # runs inside of pytest function fixture scope
+    # after test function runs
 
+    from sqlalchemy.testing import asyncio
 
-def test_teardown(item):
-    plugin_base.after_test(item)
+    asyncio._maybe_async(plugin_base.after_test, item)
 
 
-def class_setup(item):
+@pytest.fixture(scope="class")
+def setup_class_methods(request):
     from sqlalchemy.testing import asyncio
 
-    asyncio._maybe_async_provisioning(plugin_base.start_test_class, item.cls)
+    cls = request.cls
+
+    if hasattr(cls, "setup_test_class"):
+        asyncio._maybe_async(cls.setup_test_class)
+
+    if py2k:
+        reinvent_fixtures_py2k.run_class_fixture_setup(request)
+
+    yield
+
+    if py2k:
+        reinvent_fixtures_py2k.run_class_fixture_teardown(request)
 
+    if hasattr(cls, "teardown_test_class"):
+        asyncio._maybe_async(cls.teardown_test_class)
 
-def class_teardown(item):
-    plugin_base.stop_test_class(item.cls)
+    asyncio._maybe_async(plugin_base.stop_test_class, cls)
+
+
+@pytest.fixture(scope="function")
+def setup_test_methods(request):
+    from sqlalchemy.testing import asyncio
+
+    # called for each test
+
+    self = request.instance
+
+    # 1. run outer xdist-style setup
+    if hasattr(self, "setup_test"):
+        asyncio._maybe_async(self.setup_test)
+
+    # alembic test suite is using setUp and tearDown
+    # xdist methods; support these in the test suite
+    # for the near term
+    if hasattr(self, "setUp"):
+        asyncio._maybe_async(self.setUp)
+
+    # 2. run homegrown function level "autouse" fixtures under py2k
+    if py2k:
+        reinvent_fixtures_py2k.run_fn_fixture_setup(request)
+
+    # inside the yield:
+
+    # 3. function level "autouse" fixtures under py3k (examples: TablesTest
+    #    define tables / data, MappedTest define tables / mappers / data)
+
+    # 4. function level fixtures defined on test functions themselves,
+    #    e.g. "connection", "metadata" run next
+
+    # 5. pytest hook pytest_runtest_call then runs
+
+    # 6. test itself runs
+
+    yield
+
+    # yield finishes:
+
+    # 7. pytest hook pytest_runtest_teardown hook runs, this is associated
+    #    with fixtures close all sessions, provisioning.stop_test_class(),
+    #    engines.testing_reaper -> ensure all connection pool connections
+    #    are returned, engines created by testing_engine that aren't the
+    #    config engine are disposed
+
+    # 8. function level fixtures defined on test functions
+    #    themselves, e.g. "connection" rolls back the transaction, "metadata"
+    #    emits drop all
+
+    # 9. function level "autouse" fixtures under py3k (examples: TablesTest /
+    #    MappedTest delete table data, possibly drop tables and clear mappers
+    #    depending on the flags defined by the test class)
+
+    # 10. run homegrown function-level "autouse" fixtures under py2k
+    if py2k:
+        reinvent_fixtures_py2k.run_fn_fixture_teardown(request)
+
+    asyncio._maybe_async(plugin_base.after_test_fixtures, self)
+
+    # 11. run outer xdist-style teardown
+    if hasattr(self, "tearDown"):
+        asyncio._maybe_async(self.tearDown)
+
+    if hasattr(self, "teardown_test"):
+        asyncio._maybe_async(self.teardown_test)
 
 
 def getargspec(fn):
@@ -461,6 +558,8 @@ def %(name)s(%(args)s):
             # for the wrapped function
             decorated.__module__ = fn.__module__
             decorated.__name__ = fn.__name__
+            if hasattr(fn, "pytestmark"):
+                decorated.pytestmark = fn.pytestmark
             return decorated
 
     return decorate
@@ -470,6 +569,11 @@ class PytestFixtureFunctions(plugin_base.FixtureFunctions):
     def skip_test_exception(self, *arg, **kw):
         return pytest.skip.Exception(*arg, **kw)
 
+    def mark_base_test_class(self):
+        return pytest.mark.usefixtures(
+            "setup_class_methods", "setup_test_methods"
+        )
+
     _combination_id_fns = {
         "i": lambda obj: obj,
         "r": repr,
@@ -647,8 +751,18 @@ class PytestFixtureFunctions(plugin_base.FixtureFunctions):
                 fn = asyncio._maybe_async_wrapper(fn)
             # other wrappers may be added here
 
-            # now apply FixtureFunctionMarker
-            fn = fixture(fn)
+            if py2k and "autouse" in kw:
+                # py2k workaround for too-slow collection of autouse fixtures
+                # in pytest 4.6.11.  See notes in reinvent_fixtures_py2k for
+                # rationale.
+
+                # comment this condition out in order to disable the
+                # py2k workaround entirely.
+                reinvent_fixtures_py2k.add_fixture(fn, fixture)
+            else:
+                # now apply FixtureFunctionMarker
+                fn = fixture(fn)
+
             return fn
 
         if fn:
diff --git a/lib/sqlalchemy/testing/plugin/reinvent_fixtures_py2k.py b/lib/sqlalchemy/testing/plugin/reinvent_fixtures_py2k.py
new file mode 100644
index 000000000..36b68417b
--- /dev/null
+++ b/lib/sqlalchemy/testing/plugin/reinvent_fixtures_py2k.py
@@ -0,0 +1,112 @@
+"""
+invent a quick version of pytest autouse fixtures as pytest's unacceptably slow
+collection/high memory use in pytest 4.6.11, which is the highest version that
+works in py2k.
+
+by "too-slow" we mean the test suite can't even manage to be collected for a
+single process in less than 70 seconds or so and memory use seems to be very
+high as well.   for two or four workers the job just times out after ten
+minutes.
+
+so instead we have invented a very limited form of these fixtures, as our
+current use of "autouse" fixtures are limited to those in fixtures.py.
+
+assumptions for these fixtures:
+
+1. we are only using "function" or "class" scope
+
+2. the functions must be associated with a test class
+
+3. the fixture functions cannot themselves use pytest fixtures
+
+4. the fixture functions must use yield, not return
+
+When py2k support is removed and we can stay on a modern pytest version, this
+can all be removed.
+
+
+"""
+import collections
+
+
+_py2k_fixture_fn_names = collections.defaultdict(set)
+_py2k_class_fixtures = collections.defaultdict(
+    lambda: collections.defaultdict(set)
+)
+_py2k_function_fixtures = collections.defaultdict(
+    lambda: collections.defaultdict(set)
+)
+
+_py2k_cls_fixture_stack = []
+_py2k_fn_fixture_stack = []
+
+
+def add_fixture(fn, fixture):
+    assert fixture.scope in ("class", "function")
+    _py2k_fixture_fn_names[fn.__name__].add((fn, fixture.scope))
+
+
+def scan_for_fixtures_to_use_for_class(item):
+    test_class = item.parent.parent.obj
+
+    for name in _py2k_fixture_fn_names:
+        for fixture_fn, scope in _py2k_fixture_fn_names[name]:
+            meth = getattr(test_class, name, None)
+            if meth and meth.im_func is fixture_fn:
+                for sup in test_class.__mro__:
+                    if name in sup.__dict__:
+                        if scope == "class":
+                            _py2k_class_fixtures[test_class][sup].add(meth)
+                        elif scope == "function":
+                            _py2k_function_fixtures[test_class][sup].add(meth)
+                        break
+                break
+
+
+def run_class_fixture_setup(request):
+
+    cls = request.cls
+    self = cls.__new__(cls)
+
+    fixtures_for_this_class = _py2k_class_fixtures.get(cls)
+
+    if fixtures_for_this_class:
+        for sup_ in cls.__mro__:
+            for fn in fixtures_for_this_class.get(sup_, ()):
+                iter_ = fn(self)
+                next(iter_)
+
+                _py2k_cls_fixture_stack.append(iter_)
+
+
+def run_class_fixture_teardown(request):
+    while _py2k_cls_fixture_stack:
+        iter_ = _py2k_cls_fixture_stack.pop(-1)
+        try:
+            next(iter_)
+        except StopIteration:
+            pass
+
+
+def run_fn_fixture_setup(request):
+    cls = request.cls
+    self = request.instance
+
+    fixtures_for_this_class = _py2k_function_fixtures.get(cls)
+
+    if fixtures_for_this_class:
+        for sup_ in reversed(cls.__mro__):
+            for fn in fixtures_for_this_class.get(sup_, ()):
+                iter_ = fn(self)
+                next(iter_)
+
+                _py2k_fn_fixture_stack.append(iter_)
+
+
+def run_fn_fixture_teardown(request):
+    while _py2k_fn_fixture_stack:
+        iter_ = _py2k_fn_fixture_stack.pop(-1)
+        try:
+            next(iter_)
+        except StopIteration:
+            pass