intellij doesn't autocomplete on tests directory

I got the following project:

.
├── lib
│   ├── apiguardian-api-1.1.0.jar
│   ├── junit-jupiter-api-5.6.0-M1.jar
│   ├── junit-platform-commons-1.6.0-M1.jar
│   └── opentest4j-1.2.0.jar
├── production
│   └── mavnat-fibonacci-heap
│   ├── apiguardian-api-1.1.0.jar
│   ├── FibonacciHeap.class
│   ├── FibonacciHeap$HeapNode.class
│   ├── junit-jupiter-api-5.6.0-M1.jar
│   ├── junit-platform-commons-1.6.0-M1.jar
│   ├── META-INF
│   │   └── mavnat-fibonacci-heap.kotlin_module
│   └── opentest4j-1.2.0.jar
├── src
│   └── FibonacciHeap.java
└── test
├── FibonacciHeapInsertTest.java
└── mavnat-fibonacci-heap

7 directories, 14 files

whenever I try to write in tests, for example in FibonacciHeapInsertTest.java, auto complete doesn't work for classes in src, for example in FibonacciHeap.java.

How can I solve it?