Factories an extremely useful tool for testing. The more complex the use case, the more awesome you find out Laravel factories are.
For instance, we might need to create a few items, each one with a different measurement of its own:
Item::factory() //... ->has(Measurement::factory()->state(new Sequence( ['length' => 50, "width" => 110], ['length' => 65, "width" => 200], ['length' => 190, "width" => 295], ))) ->count(3) ->create()
This will result in 3 items, each item having one unique measurement assigned. The first item will have a measurement with values corresponding to the first array in the sequence and so on.