fix: test client is updated to be asyncio and not promises

resolves #1296

graphene/test/__init__.py

@@ -1,6 +1,6 @@
-from promise import Promise, is_thenable
 from graphql.error import format_error as format_graphql_error
 from graphql.error import GraphQLError
+from graphql.pyutils import is_awaitable
 
 from graphene.types.schema import Schema
 
@@ -32,7 +32,14 @@ class Client:
 
     def execute(self, *args, **kwargs):
         executed = self.schema.execute(*args, **dict(self.execute_options, **kwargs))
-        if is_thenable(executed):
+        if is_awaitable(executed):
-            return Promise.resolve(executed).then(self.format_result)
+            executed = asyncio.run(executed)
+
+        return self.format_result(executed)
+
+    async def execute_async(self, *args, **kwargs):
+        executed = self.schema.execute(*args, **dict(self.execute_options, **kwargs))
+        if is_awaitable(executed):
+            executed = await asyncio.run(executed)
 
         return self.format_result(executed)