[minor](test) Add Iceberg hadoop catalog FE unit test (#32449)

For easy testing the behavior of Iceberg's HadoopCatalog.listNamespaces()

fe/fe-core/src/main/java/org/apache/doris/fs/remote/dfs/DFSFileSystem.java

@@ -29,6 +29,7 @@ import org.apache.doris.fs.operations.OpParams;
 import org.apache.doris.fs.remote.RemoteFile;
 import org.apache.doris.fs.remote.RemoteFileSystem;
 
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.FSDataInputStream;
@@ -72,8 +73,9 @@ public class DFSFileSystem extends RemoteFileSystem {
         this.properties.putAll(properties);
     }
 
+    @VisibleForTesting
     @Override
-    protected FileSystem nativeFileSystem(String remotePath) throws UserException {
+    public FileSystem nativeFileSystem(String remotePath) throws UserException {
         if (dfsFileSystem != null) {
             return dfsFileSystem;
         }

fe/fe-core/src/test/java/org/apache/doris/external/iceberg/IcebergHadoopCatalogTest.java

@@ -0,0 +1,92 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package org.apache.doris.external.iceberg;
+
+import org.apache.doris.analysis.StorageBackend;
+import org.apache.doris.common.UserException;
+import org.apache.doris.datasource.property.PropertyConverter;
+import org.apache.doris.fs.FileSystemFactory;
+import org.apache.doris.fs.remote.dfs.DFSFileSystem;
+
+import com.google.common.collect.Maps;
+import org.apache.hadoop.fs.FileStatus;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.fs.PathFilter;
+import org.apache.hadoop.fs.RemoteIterator;
+import org.junit.Ignore;
+
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.util.Map;
+
+public class IcebergHadoopCatalogTest {
+    FileSystem nativeFs;
+    private static final PathFilter TABLE_FILTER = (path) -> path.getName().endsWith(".metadata.json");
+
+    @Ignore
+    // This logic is same as HadoopCatalog.listNamespaces in Iceberg 1.4.3.
+    // So that we can use this to test the behavior.
+    // Set correct properties to test.
+    public void testHadoopCatalogListNamespaces() throws UserException, IOException {
+        Map<String, String> properties = Maps.newHashMap();
+        properties.put("cos.access_key", "xxx");
+        properties.put("cos.secret_key", "yyy");
+        properties.put("cos.endpoint", "cos.ap-beijing.myqcloud.com");
+        properties.put("cos.region", "ap-beijing");
+        Map<String, String> hadoopProps = PropertyConverter.convertToHadoopFSProperties(properties);
+        String pathStr = "cosn://bucket1/namespace";
+        DFSFileSystem fs = (DFSFileSystem) FileSystemFactory.get("", StorageBackend.StorageType.HDFS, hadoopProps);
+        nativeFs = fs.nativeFileSystem(pathStr);
+
+        RemoteIterator<FileStatus> it = nativeFs.listStatusIterator(new Path(pathStr));
+        while (it.hasNext()) {
+            Path path = (it.next()).getPath();
+            if (isNamespace(path)) {
+                System.out.println(path);
+            }
+        }
+    }
+
+    private boolean isNamespace(Path path) throws IOException {
+        return this.isDirectory(path) && !this.isTableDir(path);
+    }
+
+    private boolean isDirectory(Path path) throws IOException {
+        try {
+            FileStatus fileStatus = this.nativeFs.getFileStatus(path);
+            return fileStatus.isDirectory();
+        } catch (FileNotFoundException var3) {
+            return false;
+        } catch (IOException var4) {
+            throw var4;
+        }
+    }
+
+    private boolean isTableDir(Path path) throws IOException {
+        Path metadataPath = new Path(path, "metadata");
+
+        try {
+            return this.nativeFs.listStatus(metadataPath, TABLE_FILTER).length >= 1;
+        } catch (FileNotFoundException var4) {
+            return false;
+        } catch (IOException var5) {
+            throw var5;
+        }
+    }
+}