core: move stuff from tests/demo.py to my/core/tests/test_config.py

also clean all this up a bit

my/core/tests/test_config.py

@@ -0,0 +1,132 @@
+"""
+Various tests that are checking behaviour of user config wrt to various things
+"""
+
+import sys
+from pathlib import Path
+
+import pytest
+import pytz
+from more_itertools import ilen
+
+import my.config
+from my.core import notnone
+from my.demo import items, make_config
+
+
+# run the same test multiple times to make sure there are not issues with import order etc
+@pytest.mark.parametrize('run_id', ['1', '2'])
+def test_override_config(tmp_path: Path, run_id: str) -> None:
+    class user_config:
+        username = f'user_{run_id}'
+        data_path = f'{tmp_path}/*.json'
+
+    my.config.demo = user_config  # type: ignore[misc, assignment]
+
+    [item1, item2] = items()
+    assert item1.username == f'user_{run_id}'
+    assert item2.username == f'user_{run_id}'
+
+
+@pytest.mark.skip(reason="won't work at the moment because of inheritance")
+def test_dynamic_config_simplenamespace(tmp_path: Path) -> None:
+    from types import SimpleNamespace
+
+    user_config = SimpleNamespace(
+        username='user3',
+        data_path=f'{tmp_path}/*.json',
+    )
+    my.config.demo = user_config  # type: ignore[misc, assignment]
+
+    cfg = make_config()
+
+    assert cfg.username == 'user3'
+
+
+def test_mixin_attribute_handling(tmp_path: Path) -> None:
+    """
+    Tests that arbitrary mixin attributes work with our config handling pattern
+    """
+
+    nytz = pytz.timezone('America/New_York')
+
+    class user_config:
+        # check that override is taken into the account
+        timezone = nytz
+
+        irrelevant = 'hello'
+
+        username = 'UUU'
+        data_path = f'{tmp_path}/*.json'
+
+    my.config.demo = user_config  # type: ignore[misc, assignment]
+
+    cfg = make_config()
+
+    assert cfg.username == 'UUU'
+
+    # mypy doesn't know about it, but the attribute is there
+    assert getattr(cfg, 'irrelevant') == 'hello'
+
+    # check that overridden default attribute is actually getting overridden
+    assert cfg.timezone == nytz
+
+    [item1, item2] = items()
+    assert item1.username == 'UUU'
+    assert notnone(item1.dt.tzinfo).zone == nytz.zone  # type: ignore[attr-defined]
+    assert item2.username == 'UUU'
+    assert notnone(item2.dt.tzinfo).zone == nytz.zone  # type: ignore[attr-defined]
+
+
+# use multiple identical tests to make sure there are no issues with cached imports etc
+@pytest.mark.parametrize('run_id', ['1', '2'])
+def test_dynamic_module_import(tmp_path: Path, run_id: str) -> None:
+    """
+    Test for dynamic hackery in config properties
+     e.g. importing some external modules
+    """
+
+    ext = tmp_path / 'external'
+    ext.mkdir()
+    (ext / '__init__.py').write_text(
+        '''
+def transform(x):
+    from .submodule import do_transform
+    return do_transform(x)
+
+'''
+    )
+    (ext / 'submodule.py').write_text(
+        f'''
+def do_transform(x):
+    return {{"total_{run_id}": sum(x.values())}}
+'''
+    )
+
+    class user_config:
+        username = 'someuser'
+        data_path = f'{tmp_path}/*.json'
+        external = f'{ext}'
+
+    my.config.demo = user_config  # type: ignore[misc, assignment]
+
+    [item1, item2] = items()
+    assert item1.raw == {f'total_{run_id}': 1 + 123}, item1
+    assert item2.raw == {f'total_{run_id}': 2 + 456}, item2
+
+    # need to reset these modules, otherwise they get cached
+    # kind of relevant to my.core.cfg.tmp_config
+    sys.modules.pop('external', None)
+    sys.modules.pop('external.submodule', None)
+
+
+@pytest.fixture(autouse=True)
+def prepare_data(tmp_path: Path):
+    (tmp_path / 'data.json').write_text(
+        '''
+[
+    {"key": 1, "value": 123},
+    {"key": 2, "value": 456}
+]
+'''
+    )