Added decorator to test availability of datasets

Used decorator tool to validate dataset exists on views

ref-test/app/tools/data.py

@@ -1,8 +1,13 @@
+from ..models import Dataset
+
 from flask import current_app as app
+from flask import flash, redirect
+from flask.helpers import url_for
 
 import json
 from pathlib import Path
 from random import shuffle
+from functools import wraps
 
 def load(filename:str):
     data_dir = Path(app.config.get('DATA'))
@@ -66,4 +71,14 @@ def get_tag_list(dataset:list):
         if block['type'] == 'question': output = list(set(output) | set(block['tags']))
         if block['type'] == 'block':
             for question in block['questions']: output = list(set(output) | set(question['tags']))
-    return output
+    return output
+
+def check_dataset_exists(function):
+    @wraps(function)
+    def wrapper(*args, **kwargs):
+        datasets = Dataset.query.all()
+        if not datasets:
+            flash('There are no available question datasets. Please upload a question dataset first, or use the question editor to create a new dataset.', 'error')
+            return redirect(url_for('admin._questions'))
+        return function(*args, **kwargs)
+    return wrapper