Simplify test by removing ThreadPool

tests/test_auth.py

@@ -1,7 +1,7 @@
 import re
 import pytest
 import tornado.web
-from concurrent.futures import ThreadPoolExecutor
+import tornado.gen
 
 
 @pytest.mark.gen_test
@@ -17,10 +17,13 @@ def test_redirects_when_not_logged_in(http_client, base_url):
 
 @pytest.mark.gen_test
 def test_login_with_valid_bearer_token(app, monkeypatch, http_client, base_url):
-    with ThreadPoolExecutor(max_workers=1) as executor:
+    @tornado.gen.coroutine
+    def _validate_login_token(c, t):
+        return True
+
     monkeypatch.setattr(
         "atst.handlers.login.Login._validate_login_token",
-            lambda c,t: executor.submit(lambda: True),
+        _validate_login_token
     )
     response = yield http_client.fetch(
         base_url + "/login?bearer-token=abc-123",