Simplest way to build a Java project with JUnit tests in it? (after being sent only src folder)

I have a Java project with src directory containing main and test (JUnit testing). I used Gradle within Intellij IDEA in development to build it, but now I have to send someone else only the src file and clear instructions how to build it and run the tests from their side.

I moved the src into a new project and I can get Gradle to work from the command line, but when I open it in Intellij it's a mess and it can't resolve anything in the test folder.

What is the simplest build tool to use on the src folder that will allow them to run it both from the command line and to open and build in in the IDE of their choosing?

Thank you!