UPDATE: This rule has been merged into PHPStan itself. Here is the PR: phpstan/phpstan-src#3294

Weirdly enough, PHPStan does not check if a file exists when used in a require or include statement. This is a PHPStan rule that tries to do exactly that.

composer require --dev bellangelo/phpstan-require-file-exists

For local development and testing, composer.json contains several commands that you can run.

• composer run tests - runs the PHPUnit tests.
• composer run phpstan - runs PHPStan on the src and tests directories.
• composer run phpcs - runs PHP CodeSniffer on the src and tests directories.
• composer run phpcs:fix - runs PHP CodeSniffer on the src and tests directories and tries to fix the issues.