Sort sets when returned into Lua

This is to match redis's documented behaviour of sorting some arrays
when Lua fetches them, to make scripts deterministic.

fakenewsredis.py

@@ -781,6 +781,12 @@ def _convert_redis_result(self, lua_runtime, result):
                 for item in result.items()
                 for i in item
             ]
+        elif isinstance(result, set):
+            converted = sorted(
+                self._convert_redis_result(lua_runtime, item)
+                for item in result
+            )
+            return lua_runtime.table_from(converted)
         elif isinstance(result, (list, set, tuple)):
             converted = [
                 self._convert_redis_result(lua_runtime, item)

test_fakenewsredis.py

@@ -3338,7 +3338,7 @@ def test_eval_lset(self):
         self.assertEqual(self.redis.lrange('foo', 0, -1), [b'z', b'b'])
 
     def test_eval_sdiff(self):
-        self.redis.sadd('foo', 'a', 'b', 'c')
+        self.redis.sadd('foo', 'a', 'b', 'c', 'f', 'e', 'd')
         self.redis.sadd('bar', 'b')
         val = self.redis.eval(
             '''
@@ -3349,7 +3349,8 @@ def test_eval_sdiff(self):
                 return value;
             end
             ''', 2, 'foo', 'bar')
-        self.assertEqual(set(val), set([b'a', b'c']))
+        # Lua must receive the set *sorted*
+        self.assertEqual(val, [b'a', b'c', b'd', b'e', b'f'])
 
 
 class TestFakeRedis(unittest.TestCase):