Junit testing - test class cannot access base class

I’m trying to do a simple unit test on a little room area calculator program.
I imported the Junit testing framework using IntelliJ idea and made a test class, but it doesn’t seem to have access to the actual class that I want to test.
The project is here on Repl.it:
[https://repl.it/@bennypr0fane/RoomAreaCalculator#Main.java](Room Area Calculator)

Error message:

 javac -classpath .:/run_dir/junit-4.12.jar:target/dependency/* -d . Main.java Room.java Test/RoomTest.java TooHighException.java TooLowException.java
Test/RoomTest.java:3: error: package org.junit.jupiter.api does not exist
import org.junit.jupiter.api.Test;
                            ^
Test/RoomTest.java:5: error: package org.junit.jupiter.api does not exist
import static org.junit.jupiter.api.Assertions.*;
                                   ^
Test/RoomTest.java:9: error: cannot find symbol
    @Test
     ^
  symbol:   class Test
  location: class RoomTest
Test/RoomTest.java:12: error: cannot find symbol
        Room room = new Room();
        ^
  symbol:   class Room
  location: class RoomTest
Test/RoomTest.java:12: error: cannot find symbol
        Room room = new Room();
                        ^
  symbol:   class Room
  location: class RoomTest
5 errors

This is what looks like locally in IntelliJ:

I suspect that I somehow need to make the Test package part of the default package - which I don’t know how to do…?
Otherwise, how would I do it so that the RoomTest class can create an instance of Room class?