Add database migrations

- use Alembic to migrate the PostgreSQL database
  + create initial migration script to set up the database,
    as an alternative to db.Base.metadata.create_all()
  + integrate Alembic into the test suite; the db_engine fixture
    now has two modes:
    * create the latest version of tables all at once
    * invoke `alembic upgrade head`
    => the "e2e" tests are all run twice, once in each mode; this
       ensures that the migration scripts re-create the same database
       schema as db.Base.metadata.create_all() would
    * in both modes, a temporary PostgreSQL schema is used to create the
      tables in
    => could now run "e2e" tests against production database and still
       have isolation
- make the configuration module public (to be used by Alembic)
- adjust linting rules for Alembic

tests/test_config.py

@@ -2,7 +2,7 @@
 
 import pytest
 
-from urban_meal_delivery import _config as config_mod  # noqa:WPS450
+from urban_meal_delivery import configuration
 
 
 envs = ['production', 'testing']
@@ -11,7 +11,7 @@ envs = ['production', 'testing']
 @pytest.mark.parametrize('env', envs)
 def test_config_repr(env):
     """Config objects have the text representation '<configuration>'."""
-    config = config_mod.get_config(env)
+    config = configuration.make_config(env)
 
     assert str(config) == '<configuration>'
 
@@ -19,18 +19,18 @@ def test_config_repr(env):
 def test_invalid_config():
     """There are only 'production' and 'testing' configurations."""
     with pytest.raises(ValueError, match="'production' or 'testing'"):
-        config_mod.get_config('invalid')
+        configuration.make_config('invalid')
 
 
 @pytest.mark.parametrize('env', envs)
 def test_database_uri_set(env, monkeypatch):
     """Package does NOT emit warning if DATABASE_URI is set."""
     uri = 'postgresql://user:password@localhost/db'
-    monkeypatch.setattr(config_mod.ProductionConfig, 'DATABASE_URI', uri)
-    monkeypatch.setattr(config_mod.TestingConfig, 'DATABASE_URI', uri)
+    monkeypatch.setattr(configuration.ProductionConfig, 'DATABASE_URI', uri)
+    monkeypatch.setattr(configuration.TestingConfig, 'DATABASE_URI', uri)
 
     with pytest.warns(None) as record:
-        config_mod.get_config(env)
+        configuration.make_config(env)
 
     assert len(record) == 0  # noqa:WPS441,WPS507
 
@@ -38,16 +38,17 @@ def test_database_uri_set(env, monkeypatch):
 @pytest.mark.parametrize('env', envs)
 def test_no_database_uri_set(env, monkeypatch):
     """Package does not work without DATABASE_URI set in the environment."""
-    monkeypatch.setattr(config_mod.ProductionConfig, 'DATABASE_URI', None)
-    monkeypatch.setattr(config_mod.TestingConfig, 'DATABASE_URI', None)
+    monkeypatch.setattr(configuration.ProductionConfig, 'DATABASE_URI', None)
+    monkeypatch.setattr(configuration.TestingConfig, 'DATABASE_URI', None)
 
     with pytest.warns(UserWarning, match='no DATABASE_URI'):
-        config_mod.get_config(env)
+        configuration.make_config(env)
 
 
 def test_random_testing_schema():
-    """CLEAN_SCHEMA is randomized if not seti explicitly."""
-    result = config_mod.random_schema_name()
+    """CLEAN_SCHEMA is randomized if not set explicitly."""
+    result = configuration.random_schema_name()
 
     assert isinstance(result, str)
-    assert len(result) <= 10
+    assert result.startswith('temp_')
+    assert len(result) == 15