tests: simplify tests for my.core.serialize a bit and simplify tox file

tox.ini

@@ -34,14 +34,11 @@ commands =
 commands =
     {envpython} -m pip install --use-pep517 -e .[testing]
     
-    # seems that denylist tests rely on it? ideally we should get rid of this in tests-core
-    {envpython} -m pip install orjson
-
     {envpython} -m pytest \
         # 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            \
+        --pyargs {[testenv]package_name}.core  \
         # ignore orgmode because it imports orgparse
         # tbh not sure if it even belongs to core, maybe move somewhere else..
         # same with pandas?
@@ -49,9 +46,6 @@ commands =
         # 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}
 
 
@@ -63,14 +57,7 @@ setenv = MY_CONFIG = nonexistent
 commands =
     {envpython} -m pip install --use-pep517 -e .[testing]
 
-    # installed to test my.core.serialize while using simplejson and not orjson
-    {envpython} -m pip install simplejson
-    {envpython} -m pytest \
-        tests/serialize_simplejson.py \
-        {posargs}
-
     {envpython} -m pip install cachew
-    {envpython} -m pip install orjson
 
     {envpython} -m my.core module install my.location.google
     {envpython} -m pip install ijson # optional dependency
@@ -103,9 +90,7 @@ commands =
     {envpython} -m pytest tests \
         # ignore some tests which might take a while to run on ci..
         --ignore tests/takeout.py        \
-        --ignore tests/extra/polar.py \
-        # dont run simplejson compatibility test since orjson is now installed
-        --ignore tests/serialize_simplejson.py \
+        --ignore tests/extra/polar.py
         {posargs}