Add test capturing expectation that the password prompt occurs if no …

…password was indicated. Ref #426 #450.

tests/test_utils.py

@@ -249,6 +249,12 @@ def get_password(system, user):
     assert pw == 'entered pw'
 
 
+def test_no_password_defers_to_prompt(monkeypatch):
+    monkeypatch.setattr(utils, 'password_prompt', lambda prompt: 'entered pw')
+    pw = utils.get_password('system', 'user', None, {'password': None})
+    assert pw == 'entered pw'
+
+
 def test_get_username_and_password_keyring_overrides_prompt(monkeypatch):
     import collections
     Credential = collections.namedtuple('Credential', 'username password')