Add basic test for DevDocNeeded model (#661)

Fixes #435

tests/test_devdocneeded.py

@@ -0,0 +1,14 @@
+# -*- coding: utf-8 -*-
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this file,
+# You can obtain one at http://mozilla.org/MPL/2.0/.
+
+from bugbug.models.devdocneeded import DevDocNeededModel
+
+
+def test_get_devdocneeded_labels():
+    model = DevDocNeededModel()
+    classes, _ = model.get_labels()
+    assert classes[528988] == 0
+    assert classes[1053944] == 1
+    assert classes[1531080] == 1