add comments

Author: Apache9

hbase-server/src/test/java/org/apache/hadoop/hbase/wal/TestParsePartialWALFile.java

@@ -52,6 +52,20 @@
 import org.junit.Test;
 import org.junit.experimental.categories.Category;
 
+/**
+ * In this test, we write a small WAL file first, and then generate partial WAL file which length is
+ * in range [0, fileLength)(we test all the possible length in the range), to see if we can
+ * successfully get the completed entries, and also get an EOF at the end.
+ * <p/>
+ * It is very important to make sure 3 things:
+ * <ul>
+ * <li>We do not get incorrect entries. Otherwise there will be data corruption.</li>
+ * <li>We can get all the completed entries, i.e, we do not miss some data. Otherwise there will be
+ * data loss.</li>
+ * <li>We will get an EOF finally, instead of a general IOException. Otherwise the split or
+ * replication will be stuck.</li>
+ * </ul>
+ */
 @Category({ RegionServerTests.class, MediumTests.class })
 public class TestParsePartialWALFile {