update unit tests

Author: Dan Choi

tests/unit/test_image.py

@@ -537,22 +537,20 @@ def test_prepare_serving_volumes_with_local_model(get_data_source_instance, sage
 
 def test_ecr_login_non_ecr():
     session_mock = Mock()
-    result = sagemaker.local.image._ecr_login_if_needed(session_mock, 'ubuntu')
+    sagemaker.local.image._ecr_login_if_needed(session_mock, 'ubuntu')
 
     session_mock.assert_not_called()
-    assert result is False
 
 
 @patch('sagemaker.local.image._check_output', return_value='123451324')
 def test_ecr_login_image_exists(_check_output):
     session_mock = Mock()
 
     image = '520713654638.dkr.ecr.us-east-1.amazonaws.com/image-i-have:1.0'
-    result = sagemaker.local.image._ecr_login_if_needed(session_mock, image)
+    sagemaker.local.image._ecr_login_if_needed(session_mock, image)
 
     session_mock.assert_not_called()
     _check_output.assert_called()
-    assert result is False
 
 
 @patch('subprocess.check_output', return_value=''.encode('utf-8'))