The SitePoint PHP blog has a quick tutorial posted helping you get your application PHP 7 ready with the help of the PhpCompatibility "sniffs" for the widely used PHP_CodeSniffer tool.
Sooner or later, there will come a time when you will need to migrate your projects to different PHP versions. How will you check if you’re compatible with a PHP version different to the one you’ve been developing on?
One possibility is always to install the version of PHP we want to migrate to, run php -l or something like PHPSA to check for syntax errors, check the PHP documentation for known issues with the migration and hope for the best. Or, we can use some available third party tools to check for PHP version compatibility in our projects.
The article then introduces the PHPCompatibility set of sniffs for PHP_CodeSniffer and installing them with a "git clone" in the right Standards directory. Also included are some basics for using PHP_CodeSniffer (like the command line options) and an example of some of the output from the compatibility check. The post wraps up with a real-life example using the PHPMailer codebase and testing it for PHP 5.6 readiness.