import unittest
import alembic.command
from mailman.database.alembic import alembic_cfg
class TestMigrations(unittest.TestCase):
    layer = ConfigLayer
    def setUp(self):
        alembic.command.stamp(alembic_cfg, 'head')
    def test_all_migrations(self):
        script_dir = alembic.script.ScriptDirectory.from_config(alembic_cfg)
        revisions = [sc.revision for sc in script_dir.walk_revisions()]
        with catch_warnings():
            simplefilter('ignore', UserWarning)
            # Alembic/SQLite does not like something about these migrations.
            # They're more or less inconsequential in practice (since users
            # will rarely if ever downgrade their database), but it does
            # clutter up the test output, so just suppress the warning.
            #
            # E.g.
            # alembic/util/messaging.py:69: UserWarning:
            # Skipping unsupported ALTER for creation of implicit constraint
            for revision in revisions:
                alembic.command.downgrade(alembic_cfg, revision)
            revisions.reverse()
            for revision in revisions:
                alembic.command.upgrade(alembic_cfg, revision)

from alembic.config import Config
from contextlib import ExitStack
from mailman.utilities.modules import expand_path
from public import public
with ExitStack() as resources:
    cfg_path = expand_path(resources, 'python:mailman.config.alembic')
    public(alembic_cfg=Config(cfg_path))

Traceback (most recent call last):
  File "/var/MM/3/na/mailman/.tox/py37-nocov/lib/python3.7/site-packages/alembic/script/base.py", line 171, in _catch_revision_errors
    yield
  File "/var/MM/3/na/mailman/.tox/py37-nocov/lib/python3.7/site-packages/alembic/script/base.py", line 386, in _downgrade_revs
    for script in revs
  File "/var/MM/3/na/mailman/.tox/py37-nocov/lib/python3.7/site-packages/alembic/script/base.py", line 383, in <listcomp>
    migration.MigrationStep.downgrade_from_script(
  File "/var/MM/3/na/mailman/.tox/py37-nocov/lib/python3.7/site-packages/alembic/script/revision.py", line 711, in iterate_revisions
    assert_relative_length=assert_relative_length,
  File "/var/MM/3/na/mailman/.tox/py37-nocov/lib/python3.7/site-packages/alembic/script/revision.py", line 1212, in _collect_downgrade_revisions
    "Not a valid downgrade target from current heads"
alembic.script.revision.RevisionError: Not a valid downgrade target from current heads
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
  File "/var/MM/3/na/mailman/src/mailman/database/tests/test_migrations.py", line 78, in test_all_migrations
    alembic.command.downgrade(alembic_cfg, revision)
  File "/var/MM/3/na/mailman/.tox/py37-nocov/lib/python3.7/site-packages/alembic/command.py", line 335, in downgrade
    script.run_env()
  File "/var/MM/3/na/mailman/.tox/py37-nocov/lib/python3.7/site-packages/alembic/script/base.py", line 490, in run_env
    util.load_python_file(self.dir, "env.py")
  File "/var/MM/3/na/mailman/.tox/py37-nocov/lib/python3.7/site-packages/alembic/util/pyfiles.py", line 97, in load_python_file
    module = load_module_py(module_id, path)
  File "/var/MM/3/na/mailman/.tox/py37-nocov/lib/python3.7/site-packages/alembic/util/compat.py", line 182, in load_module_py
    spec.loader.exec_module(module)
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/var/MM/3/na/mailman/src/mailman/database/alembic/env.py", line 76, in <module>
    run_migrations_online()
  File "/var/MM/3/na/mailman/src/mailman/database/alembic/env.py", line 70, in run_migrations_online
    context.run_migrations()
  File "<string>", line 8, in run_migrations
  File "/var/MM/3/na/mailman/.tox/py37-nocov/lib/python3.7/site-packages/alembic/runtime/environment.py", line 813, in run_migrations
    self.get_context().run_migrations(**kw)
  File "/var/MM/3/na/mailman/.tox/py37-nocov/lib/python3.7/site-packages/alembic/runtime/migration.py", line 549, in run_migrations
    for step in self._migrations_fn(heads, self):
  File "/var/MM/3/na/mailman/.tox/py37-nocov/lib/python3.7/site-packages/alembic/command.py", line 324, in downgrade
    return script._downgrade_revs(revision, rev)
  File "/var/MM/3/na/mailman/.tox/py37-nocov/lib/python3.7/site-packages/alembic/script/base.py", line 386, in _downgrade_revs
    for script in revs
  File "/usr/local/lib/python3.7/contextlib.py", line 130, in __exit__
    self.gen.throw(type, value, traceback)
  File "/var/MM/3/na/mailman/.tox/py37-nocov/lib/python3.7/site-packages/alembic/script/base.py", line 205, in _catch_revision_errors
    compat.raise_(util.CommandError(err.args[0]), from_=err)
  File "/var/MM/3/na/mailman/.tox/py37-nocov/lib/python3.7/site-packages/alembic/util/compat.py", line 294, in raise_
    raise exception
alembic.util.exc.CommandError: Not a valid downgrade target from current heads