tox: do not try to find .ipynbs using 'find' as subshells not permitt…

…ed in tox.ini

tox.ini

@@ -12,6 +12,8 @@ whitelist_externals =
     test
     wc
     make
+    xargs
+    find
 commands = 
     ; Ensure ipywidgets Jupyter extension is installed
     jupyter nbextension enable --py --sys-prefix widgetsnbextension
@@ -25,7 +27,8 @@ commands =
 
     ; Ensure test and demo Notebooks runs *without errors* (do not check for regressions yet)
     ; (add --nbdime if running tox locally and want to visualise/explore diffs in web browser)
-    pytest --verbose --maxfail=1 --nbval-lax --nbval-cell-timeout=120 --cov-config=tox.ini --cov="{envsitepackagesdir}/mumot" --cov-append $(find TestNotebooks DemoNotebooks -type f -name '*.ipynb')
+    pytest --verbose --maxfail=1 --nbval-lax --nbval-cell-timeout=120 --cov-config=tox.ini --cov="{envsitepackagesdir}/mumot" --cov-append \
+        TestNotebooks/*.ipynb TestNotebooks/MiscTests/*.ipynb DemoNotebooks/*
 
     ; Ensure the user manual and regression test Notebooks do not show regressions (TODO; leave commented)
     ; (add --nbdime if running tox locally and want to visualise/explore diffs in web browser)