Hi,<br><br>1 - I had send a PR on histogram backprojection. at that time travis build was successful. <br><br>Then i made some modifications for PEP8, but travis build shows errors which i don't understand. https://travis-ci.org/scikit-image/scikit-image/jobs/6472929.<br><br>But i haven't changed any functionality of code and it works fine in my system as good as old.<br><br>2 - Also, I didn't get the concept of writing of tests for my code. What actually the tests do and how should I write a good test code?<br><br>Regards<br>Abid K<br>