Add test for postBuild script

tests/venv/postBuild/postBuild

@@ -0,0 +1,2 @@
+#!/bin/bash
+jupyter nbextension enable --py --sys-prefix ipyleaflet

tests/venv/postBuild/requirements.txt

@@ -0,0 +1 @@
+ipyleaflet

tests/venv/postBuild/verify

@@ -0,0 +1,3 @@
+#!/bin/bash
+set -e
+jupyter nbextension list | grep 'jupyter-leaflet' | grep enabled