test walkthrough

test_find_newest_artifact.py

@patch('boto3.client') # Mock the boto3.client call to prevent using the boto3 library
def test_find_newest_artifact(mock_client): # Because we used the @patch decorator we need to add an argument for our mock'd client call
    """
    test find_newest_artifact returns a properly formatted string
    """
    # The normal "list_objects" function will return a dict.
    # One key in the dict is "Contents" which is an list of the bucket objects.
    # Each item in the "Contents" list has several keys, but if you look at the "find_newest_artifact" 
    # there are only two we are interested in:  "Key" and "LastModified".  So we need to fake a
    # "list_objects" call and return a slimmed down version of the response we expect.
    bucket_objects = {
        "Contents": [
            {
                "Key": "blah",
                "LastModified": "datetime.datetime(2016, 3, 18, 19, 20, 29, tzinfo=tzutc())"
            }
        ]
    }
    
    # Create a MagicMock object to return instead of a normal boto3.client call
    aws_s3 = MagicMock()
    mock_client.return_value = aws_s3
    
    # Using our fake object, we will now fake a list_objects call and return our
    # slimmed down response that we created above.  We don't need to fake anything 
    # else now because our slimmed down response contains everything the rest of
    # the normal logic in the function needs in order to work.
    aws_s3.list_objects.return_value = bucket_objects
    
    # Now we come to the test.  We'll pass in a fake bucket name to the function 
    # and since we set "Key" above to "blah" we should expect that our function
    # will return s3://blah/blah as the full name of the artifact.
    assert find_newest_artifact('blah') == 's3://blah/blah'