TJ Miller has written up a post for his site sharing a method he's created to verify the compatibility of a package in Laravel based on the version of Laravel installed.

I’ve been working with Honeybadger to build a new set of PHP integrations. I would like to write more about that soon, however, I feel like I’ve stumbled across something that could be useful to others. I wanted to share it as soon as I could.

For the Laravel package, I was aiming for Laravel 5.5 and newer support as it is the latest LTS version. [...] In hindsight, I don’t think that I actually ever tested it against a 5.5 install. I relied on the CI process to make those verifications for me.

[...] As Laravel 5.7 is now out, I needed to add support to both the package’s composer configuration and verification in CI. [...] Now that I am supporting three versions I felt that I needed a more specific way of verifying compatibility with different versions of Laravel.

He shares his initial version of his Travis-CI configuration, running tests on PHP 7.1 and 7.2 with the prefer-lowest flag. In order to make it easier, he updated this based on what he'd seen in other packages: adding a matrix that runs PHP 7.1 through 7.3 against versions 5.5.x, 5.6.x and 5.7.x to ensure compatibility across all variations. His resulting build looks something like this.