more debugging and catch md misconfigured error

tests/test_factory.py

@@ -68,3 +68,12 @@ def test_favicon_override():
     response = client.get('/no-title')
     assert response.status_code == 200
     assert b'<link rel="icon" href="/media/foo.png">' in response.data
+
+
+def test_misconfigured_markdown_extensions():
+    """Test that a misconfigured markdown extensions leads to a 500 at render time."""
+    instance_path = os.path.join(HERE, 'instance')
+    app = create_app(instance_path=instance_path, test_config={'MARKDOWN_EXTENSIONS': 'WRONG'})
+    client = app.test_client()
+    response = client.get('/no-title')
+    assert response.status_code == 500