#In your application

In your application you'll use most of the time the Filesystem adapter but in your tests writing to the filesystem can be slow. Instead you can use the InMemory adapter.

use Innmind\Filesystem\Adapter\InMemory;

$filesystem = InMemory::new();
// use $filesystem as usual

This adapter is tested against the same properties as Filesystem to make sure there is no divergence of behaviour between the two.