general: move most core tests inside my.core.tests package

- distributes tests alongside the package, might be convenient for package users
- removes some weird indirection (e.g. dummy test files improting tests from modules)
- makes the command line for tests cleaner (e.g. no need to remember to manually add files to tox.ini)
- tests automatically covered by mypy (so makes mypy runs cleaner and ultimately better coverage)

The (vague) convention is

- tests/somemodule.py -- testing my.core.somemodule, contains tests directly re
- tests/test_something.py -- testing a specific feature, e.g. test_get_files.py tests get_files methon only

tox.ini

@@ -19,12 +19,26 @@ passenv =
 [testenv:tests-core]
 commands =
     pip install -e .[testing]
+    
+    # seems that denylist tests rely on it? ideally we should get rid of this in tests-core
+    pip install orjson
+
     {envpython} -m pytest \
-                      tests/core.py            \
-                      tests/sqlite.py          \
-                      tests/get_files.py       \
-                      tests/test_tmp_config.py \
-                      {posargs}
+        # importlib is the new suggested import-mode
+        # without it test package names end up as core.tests.* instead of my.core.tests.*
+        --import-mode=importlib     \
+        --pyargs my.core            \
+        # ignore orgmode because it imports orgparse
+        # tbh not sure if it even belongs to core, maybe move somewhere else..
+        # same with pandas?
+        --ignore my/core/orgmode.py \
+        # causes error during test collection on 3.8
+        # dataset is deprecated anyway so whatever
+        --ignore my/core/dataset.py \
+        # this test uses orjson which is an optional dependency
+        # it would be covered by tests-all
+        -k 'not test_nt_serialize' \
+        {posargs}
 
 
 # todo maybe also have core tests and misc tests? since ideally want them without dependencies
@@ -94,11 +108,6 @@ commands =
                     {posargs}
     cat .coverage.mypy-core/index.txt
 
-    # todo hmm might be better to move modules test in a separate subpackage?
-    {envpython} -m mypy --install-types --non-interactive \
-                    tests \
-                    --exclude 'tests/(bluemaestro|emfit|takeout|pdfs|jawbone).py'
-
 
 # specific modules that are known to be mypy compliant (to avoid false negatives)
 # todo maybe split into separate jobs? need to add comment how to run