how to mock get function laravel 5.1 ?

I have this function in laravel 5.1

  { 
        if ($request->ajax()) {
        if(!in_array($loc, config('loc.available'))) {
            return response()->json([
                'status' => 'ERROR',
                'message' => 'Not available loc'
            ]);
        }
        Session::put('loc', $loc);

        return response()->json([
            'status' => 'OK',
            'loc' => $loc,
        ]);
    }

how to write mock test for this function to get passing ?

via Chebli Mohamed