unable to load webpage while using casperJS scripts on TravisCI?

I want to execute CasperJS test scripts on travisCI. I was able to install the dependencies but when I executed the script, all the tests got failed. I used below command to trigger casperjs test

sudo xvfb-run -a casperjs test --engine=slimerjs test_name.js 

Below is the error message that I got. It seems the web page didn't get loaded here

The CasperJS was trying access the web application via github. For that it needs github client id and client secret configured with web application. The webpage got loaded after configuring the Github client id and Client secret in the conf file of the application