On the next page, Select "MyProject" source folder and click Add Folder....
In New Source Folder dialog, type "sources" in the Folder name field.
Click Yes in confirmation dialog to have "MyProject/bin" as your default output folder.
Click again on Add Folder....
In Source Folder Selection, click on Create New Folder....
In New Folder dialog, type "tests" in the Folder name field.
Your project setup now looks as follows:
Working with build paths
Creating a new Java project
Creating a Java project with source folders
Creating a new source folder
Using the Package Explorer