Error when setting up phpunit tests with wp-cli scaffold

I am trying to figure out the setup for unit tests for wordpress plugins. I am using Ubuntu. So far I have:

• Local WordPress Installation
• WP-CLI up and running
• Installed phpunit
• used wp scaffold command to generate unit test files

When I now try and run the phpunit command I get the following error:

PHP Warning:  require_once(/tmp/wordpress//wp-includes/class-       phpmailer.php): failed to open stream: No such file or directory in  /tmp/wordpress-tests-lib/includes/mock-mailer.php on line 2

PHP Fatal error: require_once(): Failed opening required '/tmp/wordpress//wp-includes/class-phpmailer.php' (include_path='.:/usr/share/php:/usr/share/pear') in /tmp/wordpress-tests-lib/includes/mock-mailer.php on line 2

This is my wp --info:

PHP binary: /usr/bin/php5
PHP version:    5.6.11-1ubuntu3.4
php.ini used:   /etc/php5/cli/php.ini
WP-CLI root dir:    phar://wp-cli.phar
WP-CLI packages dir:    
WP-CLI global config:   
WP-CLI project config:  
WP-CLI version: 1.0.0

I am trying to follow this tutorial:

https://pippinsplugins.com/unit-tests-wordpress-plugins-setting-up-testing-suite/

Thank you for any help!!!