diff --git a/my/core/core_config.py b/my/core/core_config.py
index 5c7843d..c4f8ec0 100644
--- a/my/core/core_config.py
+++ b/my/core/core_config.py
@@ -5,15 +5,19 @@ import re
 from typing import Sequence, Optional
 
 from .common import PathIsh
+from . import warnings
 
 try:
-    # FIXME support legacy 'common'?
     from my.config import core as user_config # type: ignore[attr-defined]
 except Exception as e:
-    # make it defensive, because it's pretty commonly used and would be annoying if it breaks hpi doctor etc.
-    # this way it'll at least use the defaults
-    # TODO add high warning
-    user_config = object # type: ignore[assignment, misc]
+    try:
+        from my.config import common as user_config # type: ignore[attr-defined, assignment, misc]
+        warnings.high("'common' config section is deprecated. Please rename it to 'core'.")
+    except Exception as e2:
+        # make it defensive, because it's pretty commonly used and would be annoying if it breaks hpi doctor etc.
+        # this way it'll at least use the defaults
+        # todo actually not sure if needs a warning? Perhaps it's okay without it, because the defaults are reasonable enough
+        user_config = object # type: ignore[assignment, misc]
 
 
 from dataclasses import dataclass
@@ -55,13 +59,55 @@ class Config(user_config):
                 return not matches(disabled)
         else:
             if disabled is None:
-                # only enabled the specifid modules
+                # only enable the specified modules
                 return matches(enabled)
             else:
                 # ok, this means the config is inconsistent. better fallback onto the 'enable everything', then the user will notice?
-                # todo add medium warning?
+                warnings.medium("Both 'enabled_modules' and 'disabled_modules' are set in the config. Please only use one of them.")
                 return True
 
 
 from .cfg import make_config
 config = make_config(Config)
+
+
+### tests start
+
+def test_active_modules() -> None:
+    # todo maybe have this decorator for the whole of my.config?
+    from contextlib import contextmanager as ctx
+    @ctx
+    def reset():
+        from .cfg import override_config
+        with override_config(config) as cc:
+            cc.enabled_modules  = None
+            cc.disabled_modules = None
+            yield cc
+
+    with reset() as cc:
+        assert cc.is_module_active('my.whatever')
+        assert cc.is_module_active('my.core'    )
+        assert cc.is_module_active('my.body.exercise')
+
+    with reset() as cc:
+        cc.disabled_modules = ['my.body.*']
+        assert cc.is_module_active('my.whatever')
+        assert cc.is_module_active('my.core'    )
+        assert not cc.is_module_active('my.body.exercise')
+
+    with reset() as cc:
+        cc.enabled_modules = ['my.whatever']
+        assert cc.is_module_active('my.whatever')
+        assert not cc.is_module_active('my.core'    )
+        assert not cc.is_module_active('my.body.exercise')
+
+    with reset() as cc:
+        # if both are set, enable all
+        cc.disabled_modules = ['my.body.*']
+        cc.enabled_modules = ['my.whatever']
+        assert cc.is_module_active('my.whatever')
+        assert cc.is_module_active('my.core'    )
+        assert cc.is_module_active('my.body.exercise')
+        # todo suppress warnings during the tests?
+
+### tests end
diff --git a/tests/core.py b/tests/core.py
new file mode 100644
index 0000000..0997527
--- /dev/null
+++ b/tests/core.py
@@ -0,0 +1,14 @@
+'''
+NOTE: Sigh. it's nice to be able to define the tests next to the source code (so it serves as documentation).
+However, if you run 'pytest --pyargs my.core', it detects 'core' package name (because there is no my/__init__.py)
+(see https://docs.pytest.org/en/latest/goodpractices.html#tests-as-part-of-application-code)
+
+This results in relative imports failing (e.g. from ..kython import...).
+
+By using this helper file, pytest can detect the package name properly. A bit meh, but perhaps after kython is moved into the core,
+we can run against the tests in my.core directly.
+
+'''
+
+from my.core.core_config import *
+from my.core.error import *
diff --git a/tests/misc.py b/tests/misc.py
index 43ec617..869c276 100644
--- a/tests/misc.py
+++ b/tests/misc.py
@@ -46,10 +46,6 @@ def prepare(tmp_path: Path):
         pass
 
 
-# meh. otherwise was struggling to run directly against my.core.error...
-from my.core.error import *
-
-
 from typing import Iterable, List
 import warnings
 from my.core import warn_if_empty
diff --git a/tox.ini b/tox.ini
index ecd9679..f88bd3c 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,6 @@
 [tox]
 minversion = 3.5
-envlist = py3,mypy,mypy-modules # pylint
+envlist = py3,mypy,mypy-modules
 
 # TODO ugh. unclear how to reuse setup.cfg deps in tox
 [testenv]
@@ -13,7 +13,7 @@ commands =
     # todo these are probably not necessary anymore?
     python3 -c 'from my.config import stub as config; print(config.key)'
     python3 -c 'import my.config; import my.config.repos' # shouldn't fail at least
-    python3 -m pytest tests/misc.py tests/get_files.py tests/config.py::test_set_repo tests/config.py::test_environment_variable tests/demo.py
+    python3 -m pytest tests/core.py tests/misc.py tests/get_files.py tests/config.py::test_set_repo tests/config.py::test_environment_variable tests/demo.py
     # TODO add; once I figure out porg depdencency?? tests/config.py
     # TODO run demo.py? just make sure with_my is a bit cleverer?
     # TODO e.g. under CI, rely on installing
@@ -48,15 +48,3 @@ skip_install = true
 commands =
     pip install -e .[testing] .[optional]
     ./lint
-
-
-# TODO fix it
-# [testenv:pylint]
-# # TODO wtf????
-# changedir = {toxworkdir}/{envname}/../..
-# skip_install = true
-# commands =
-#     pip install -e .[testing]
-    # for now ignore import errors until I figure out how to import everything for CI checking..
-    # TODO FIXME ugh. fix later, after properly switched to my.config
-    # python -m pylint -E -d import-error my