test: Deque 테스트 코드 작성

Author: ksundong

yoonexample/src/test/java/deque/DequeTest.java

@@ -3,6 +3,7 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
+import exception.EmptyDequeException;
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;