test: test when no kernel spec exists

tests/app/no_kernelspec_test.py

@@ -0,0 +1,18 @@
+import pytest
+
+
+@pytest.fixture
+def non_existing_kernel_notebook(base_url):
+    return base_url + "/voila/render/no_kernelspec.ipynb"
+
+
+@pytest.fixture
+def voila_args(notebook_directory, voila_args_extra):
+    return ['--VoilaTest.root_dir=%r' % notebook_directory] + voila_args_extra
+
+
+@pytest.mark.gen_test
+def test_non_existing_kernel(http_client, non_existing_kernel_notebook):
+    response = yield http_client.fetch(non_existing_kernel_notebook)
+    assert response.code == 200
+    assert 'Executing without a kernelspec' in response.body.decode('utf-8')

tests/notebooks/no_kernelspec.ipynb

@@ -0,0 +1,29 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "print('Executing without a kernelspec')"
+   ]
+  }
+ ],
+ "metadata": {
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.6.7"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 2
+}