Q:

how to use variable inside laravel @include?

{{$one = 'testFileName'}}

@include('folder.project.$one')

A:

You can do that 
First solution
{{$one = 'folder.project.testFileName'}}

@include($one)

second solution
{{$one = 'testFileName'}}

@include("folder.project.$one")

third solution
{{$one = 'testFileName'}}

@include("folder.project." . $one)

And for define variable you can also use 
@php
    $one = 'testFileName';
@endphp

or (but it can depends of laravel version)
@php($one = 'testFileName')

