### Question:
HCatClient { public abstract void updateTableSchema(String dbName, String tableName, List<HCatFieldSchema> columnSchema) throws HCatException;  static HCatClient create(Configuration conf); abstract List<String> listDatabaseNamesByPattern(String pattern); abstract HCatDatabase getDatabase(String dbName); abstract void createDatabase(HCatCreateDBDesc dbInfo); abstract void dropDatabase(String dbName, boolean ifExists,
                                      DropDBMode mode); abstract List<String> listTableNamesByPattern(String dbName, String tablePattern); abstract HCatTable getTable(String dbName, String tableName); abstract void createTable(HCatCreateTableDesc createTableDesc); abstract void updateTableSchema(String dbName, String tableName, List<HCatFieldSchema> columnSchema); abstract void createTableLike(String dbName, String existingTblName,
                                         String newTableName, boolean ifNotExists, boolean isExternal,
                                         String location); abstract void dropTable(String dbName, String tableName,
                                   boolean ifExists); abstract void renameTable(String dbName, String oldName,
                                     String newName); abstract List<HCatPartition> getPartitions(String dbName, String tblName); abstract List<HCatPartition> getPartitions(String dbName, String tblName, Map<String, String> partitionSpec); abstract HCatPartition getPartition(String dbName, String tableName,
                                               Map<String, String> partitionSpec); abstract void addPartition(HCatAddPartitionDesc partInfo); abstract int addPartitions(List<HCatAddPartitionDesc> partInfoList); abstract void dropPartitions(String dbName, String tableName,
                                        Map<String, String> partitionSpec, boolean ifExists); abstract List<HCatPartition> listPartitionsByFilter(String dbName, String tblName,
                                                               String filter); abstract void markPartitionForEvent(String dbName, String tblName,
                                               Map<String, String> partKVs, PartitionEventType eventType); abstract boolean isPartitionMarkedForEvent(String dbName, String tblName,
                                                      Map<String, String> partKVs, PartitionEventType eventType); abstract String getDelegationToken(String owner,
                                              String renewerKerberosPrincipalName); abstract long renewDelegationToken(String tokenStrForm); abstract void cancelDelegationToken(String tokenStrForm); abstract String getMessageBusTopicName(String dbName, String tableName); abstract void close(); static final String HCAT_CLIENT_IMPL_CLASS; }### Answer:
@Test public void testUpdateTableSchema() throws Exception { try { HCatClient client = HCatClient.create(new Configuration(hcatConf)); final String dbName = "testUpdateTableSchema_DBName"; final String tableName = "testUpdateTableSchema_TableName"; client.dropDatabase(dbName, true, HCatClient.DropDBMode.CASCADE); client.createDatabase(HCatCreateDBDesc.create(dbName).build()); List<HCatFieldSchema> oldSchema = Arrays.asList(new HCatFieldSchema("foo", Type.INT, ""), new HCatFieldSchema("bar", Type.STRING, "")); client.createTable(HCatCreateTableDesc.create(dbName, tableName, oldSchema).build()); List<HCatFieldSchema> newSchema = Arrays.asList(new HCatFieldSchema("completely", Type.DOUBLE, ""), new HCatFieldSchema("new", Type.FLOAT, ""), new HCatFieldSchema("fields", Type.STRING, "")); client.updateTableSchema(dbName, tableName, newSchema); assertArrayEquals(newSchema.toArray(), client.getTable(dbName, tableName).getCols().toArray()); client.dropDatabase(dbName, false, HCatClient.DropDBMode.CASCADE); } catch (Exception exception) { LOG.error("Unexpected exception.", exception); assertTrue("Unexpected exception: " + exception.getMessage(), false); } }