feat: add quota project to base credentials class (#546)

diff --git a/tests/oauth2/test_credentials.py b/tests/oauth2/test_credentials.py
index 78b1012..69d9fbc 100644
--- a/tests/oauth2/test_credentials.py
+++ b/tests/oauth2/test_credentials.py
@@ -454,6 +454,13 @@
         cred.refresh(None)
         assert cred.token == "access_token"
 
+    def test_with_quota_project(self):
+        cred = credentials.UserAccessTokenCredentials()
+        quota_project_cred = cred.with_quota_project("project-foo")
+
+        assert quota_project_cred._quota_project_id == "project-foo"
+        assert quota_project_cred._account == cred._account
+
     @mock.patch(
         "google.oauth2.credentials.UserAccessTokenCredentials.apply", autospec=True
     )