Add tests for binder/apt.txt and binder/postBuild
ADD
tests/venv/binder-dir/apt.txt
+thiswontwork

ADD
tests/venv/binder-dir/binder/apt.txt
+gfortran

ADD
tests/venv/binder-dir/postBuild
+#!/bin/bash
+echo "This should never run"
+exit 1

MODIFY
tests/venv/binder-dir/verify
tests/venv/binder-dir/verify
#!/bin/bash
+which gfortran
test -z $(pip list | grep scipy)
jupyter nbextension list
jupyter nbextension list | grep 'jupyter-leaflet' | grep enabled

Add tests for binder/apt.txt and binder/postBuild