fix checkstyle.

Author: zhtttylz

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/util/TestCombinedHostsFileReader.java

@@ -31,8 +31,8 @@
 import org.mockito.stubbing.Answer;
 import org.mockito.Mock;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.mockito.Mockito.when;
 import org.mockito.MockitoAnnotations;