I want to link test codes and product codes

If you are using Maven, use the folder structure according to the rules like src/main/java and src/test/java.If the class name of the product code is FooBar, you should create a test class in the same package as FooBar under src/test/java under the terms FooBarTest

With Eclipse, you can go back and forth between the testing pairs (FooBar and FooBarTest) with Ctrl+9, and if there is no test class, they will ask you if you want to create a new one.

Creating product and test codes one-on-one like this is the easiest configuration for a single test.

Since the merge test cannot be done on a per-class basis, it is often created on a functional basis with a name like XxxIntegrationTest (sometimes it's a separate project).