create folder under test folder Flutter

I'm new in Flutter, i started creating unit tests and UI interface tests, if i put the tests classes under test directory everything works fine, but when i decided to separate UI and unitTest in separate folders under test folder

test/unitTest/test1.dart

test/ui/widget1.dart

I got an error

Error: Not found: 'dart:ui'

is it possible to create folders under test folder ?