JUnit 5 cannot resolve symbol Assertion. Test class not in TEST scope.

I created a JUnit5 test by clicking on "create Test" from the intention menu (light-bulb). A dialog said something like "create test on source root". I said OK (it was the only option). I also clicked on "Fix" to import JUnit5 library, and I chose "use JUnit5 of IntelliJ" (the other option was to copy JUnit to lib/).

Now, the test .java file cannot compile: "Error:(3, 36) java: package org.junit.jupiter.api does not exist".

If I do "Project structure -> Modules -> Dependencies tab", and change the JUnit5 scope from "TEST" to "Compile" it works. So I presume it is a problem with the layout of my project. I tried creating src/test/ and putting the .java file there, but it doesn't work. My project layout is as follow:

./iri.iml
./src
./src/com
./src/com/company
./src/com/company/myproj
./src/com/company/myproj/subpackage
./src/com/company/myproj/subpackage/Config.java
./src/com/company/myproj/subpackage/Log.java
./src/com/company/myproj/subpackage/Main.java
./src/com/company/myproj/subpackage/MyClass.java
./src/com/company/myproj/subpackage/MyClassTest.java
./.idea
./.idea/vcs.xml
./.idea/modules.xml
./.idea/workspace.xml
./.idea/kotlinc.xml
./.idea/misc.xml
./.idea/inspectionProfiles
./.idea/inspectionProfiles/Project_Default.xml

What should I do?

Thanks.