Add Expiration Task state test (should be sleeping after it is woken)

Author: alhusseain

server-session/src/test/java/com.iluwatar.sessionserver/AppTest.java

@@ -27,11 +27,8 @@
 import static java.lang.Thread.State.TIMED_WAITING;
 import static java.lang.Thread.State.WAITING;
 import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.mockito.Mockito.when;
-
 import java.io.IOException;
 import lombok.extern.slf4j.Slf4j;
-import org.junit.Before;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.MethodOrderer;