Move common testing functionality to a separate project

[Akirathan]

Pull Request Description

Introduce a new test-utils project, and moves the TestBase there. Moreover, TestBase is renamed to TestUtils and is no longer an abstract class.

Important Notes

test-utils project does not depend on junit, so it can be used, for example, by any benchmarks as well.

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
  Scala,
  Java,
  TypeScript,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• Unit tests have been written where possible.