Add test for get_credential with no username.

Captures missed expectation reported in #694

tests/test_cli.py

@@ -6,6 +6,7 @@
 import pytest
 
 from keyring import cli
+from keyring import credentials
 
 flatten = itertools.chain.from_iterable
 
@@ -36,6 +37,12 @@ def mocked_set():
         yield set_password
 
 
+@pytest.fixture
+def mocked_get_credential():
+    with mock.patch('keyring.cli.get_credential') as get_credential:
+        yield get_credential
+
+
 def test_set_interactive(monkeypatch, mocked_set):
     tool = cli.CommandLineTool()
     tool.service = 'svc'
@@ -64,3 +71,16 @@ def test_set_pipe_newline(monkeypatch, mocked_set):
     monkeypatch.setattr(sys.stdin, 'read', lambda: 'foo123\n')
     tool.do_set()
     mocked_set.assert_called_once_with('svc', 'usr', 'foo123')
+
+
+@pytest.mark.xfail(reason="#694")
+@pytest.mark.parametrize('format', ['json', 'plain'])
+def test_get_anonymous(monkeypatch, mocked_get_credential, format, capsys):
+    mocked_get_credential.return_value = credentials.AnonymousCredential('s3cret')
+    tool = cli.CommandLineTool()
+    tool.service = 'svc'
+    tool.username = None
+    tool.get_mode = 'creds'
+    tool.output_format = format
+    tool.do_get()
+    assert 's3cret' in capsys.readouterr().out