tests: move more tests into core, more consistent tests running in tox

tox.ini

@@ -48,9 +48,11 @@ commands =
 
 # todo maybe also have core tests and misc tests? since ideally want them without dependencies
 [testenv:tests-all]
-# deliberately set to nonexistent path to check the fallback logic
-# TODO not sure if need it?
-setenv = MY_CONFIG = nonexistent
+setenv =
+    # deliberately set to nonexistent path to check the fallback logic
+    # TODO not sure if need it?
+    MY_CONFIG=nonexistent
+    HPI_TESTS_USES_OPTIONAL_DEPS=true
 commands =
     {envpython} -m pip install --use-pep517 -e .[testing]
 
@@ -81,7 +83,7 @@ commands =
         # 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 {[testenv]package_name}.tests \
+        --pyargs {[testenv]package_name}.core {[testenv]package_name}.tests \
         {posargs}
 
     {envpython} -m pytest tests \