logback.xml should be available in the root directory of your CLASSPATH. When you start the application, the full CLASSPATH is printed from the very beginning. When I put logback.xml in /src/main/resources (Maven project), it works without any problems. Also, having it in /src/test/resources with the name logback-test.xml has a presence.
Just run:
 getClass().getClassLoader().getResource("/logback.xml"); 
And look if it will return anything or null .
If you are not working with a Maven project, open the project structure ( Ctrl + Alt + Shift + S ) and add to the modules selection folder containing logback.xml and mark it as sources (blue icon).
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