Where should I create utility classes that are used by unit tests, integration tests and functional tests?

Say I have a project that's using the standard Maven/Gradle project directory structure, with the source file directory like this:

src
├── functTest
├── integTest
├── main
└── test

What would be the best way of creating utility classes that provide methods that may be used by unit test, integration test and functional test classes? Is there a standard approach to this?

Would a suitable approach be to create a testutil folder under src and place utility classes in there?