Load default config in PlotlyTestCase.

Clean-slates each test. It doesn’t mean that the files aren’t dirty
between tests, but because `session` takes precedence, this helps a lot.

Author: theengineear

Diff for: plotly/tests/utils.py

@@ -27,6 +27,9 @@ def setUpClass(cls):
     def setUp(self):
         self.stash_session()
         self.stash_files()
+        defaults = dict(files.FILE_CONTENT[files.CREDENTIALS_FILE],
+                        **files.FILE_CONTENT[files.CONFIG_FILE])
+        session.sign_in(**defaults)
 
     def tearDown(self):
         self.restore_files()