Added decorator to test availability of datasets

Used decorator tool to validate dataset exists on views

ref-test/app/admin/views.py

@@ -2,7 +2,7 @@ from ..forms.admin import AddTimeAdjustment, CreateTest, CreateUser, DeleteUser,
 from ..models import Dataset, Entry, Test, User
 from ..tools.auth import disable_if_logged_in, require_account_creation
 from ..tools.forms import get_dataset_choices, get_time_options, send_errors_to_client
-from ..tools.data import check_is_json, validate_json
+from ..tools.data import check_dataset_exists, check_is_json, validate_json
 from ..tools.test import  answer_options, get_correct_answers
 
 from flask import abort, Blueprint, jsonify, render_template, redirect, request, send_file, session
@@ -247,15 +247,12 @@ def _download(id:str):
 @admin.route('/tests/<string:filter>/', methods=['GET'])
 @admin.route('/tests/', methods=['GET'])
 @login_required
+@check_dataset_exists
 def _tests(filter:str=None):
-    datasets = Dataset.query.all()
     tests = None
     _tests = Test.query.all()
     form = None
     now = datetime.now()
-    if not datasets:
-        flash('There are no available question datasets. Please upload a question dataset in order to set up an exam.', 'error')
-        return redirect(url_for('admin._questions'))
     if filter not in ['create','active','scheduled','expired','all']: return redirect(url_for('admin._tests', filter='active'))
     if filter == 'create':
         form = CreateTest()