Mark operations unsupported by LakeFS filesystem (#1881)

* mark append as unsupported operation

* include intellij project settings to running test from IDE

* add the content of LakeFSFileSystem.java

* Revert "include intellij project settings to running test from IDE"

This reverts commit b47341b.

clients/hadoopfs/pom.xml

@@ -39,8 +39,8 @@
         </dependency>
         <dependency>
             <groupId>org.mockito</groupId>
-            <artifactId>mockito-core</artifactId>
-            <version>3.9.0</version>
+            <artifactId>mockito-all</artifactId>
+            <version>1.10.19</version>
         </dependency>
         <dependency>
             <groupId>junit</groupId>

clients/hadoopfs/src/main/java/io/lakefs/FileSystem.java → clients/hadoopfs/src/main/java/io/lakefs/LakeFSFileSystem.java

@@ -13,9 +13,9 @@
 
 /**
  * A dummy implementation of the core Lakefs Filesystem.
- * This class implements a {@link FileSystem} that can be registered to Spark and support limited write and read actions.
+ * This class implements a {@link LakeFSFileSystem} that can be registered to Spark and support limited write and read actions.
  */
-public class FileSystem extends org.apache.hadoop.fs.FileSystem {
+public class LakeFSFileSystem extends org.apache.hadoop.fs.FileSystem {
 
     @Override
     public URI getUri() {
@@ -48,8 +48,7 @@ public FSDataOutputStream create(Path path, FsPermission fsPermission, boolean b
 
     @Override
     public FSDataOutputStream append(Path path, int i, Progressable progressable) throws IOException {
-        LOG.debug("$$$$$$$$$$$$$$$$$$$$$$$$$$$$ append $$$$$$$$$$$$$$$$$$$$$$$$$$$$ ");
-        return null;
+        throw new UnsupportedOperationException("Append is not supported by LakeFSFileSystem");
     }
 
     @Override

clients/hadoopfs/src/test/java/io/lakefs/LakeFSFileSystemTest.java

@@ -0,0 +1,35 @@
+package io.lakefs;
+
+import org.junit.After;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.io.IOException;
+import java.net.URI;
+
+public class LakeFSFileSystemTest {
+
+    LakeFSFileSystem fs;
+
+    @Before
+    public void setUp() throws Exception {
+        fs = new LakeFSFileSystem();
+    }
+
+    @After
+    public void tearDown() throws Exception {
+        fs = null;
+    }
+
+    @Test
+    public void getUri() {
+        URI u = fs.getUri();
+        Assert.assertEquals(u.toString(), "lakefs://main");
+    }
+
+    @Test(expected = UnsupportedOperationException.class)
+    public void testAppend() throws IOException {
+        fs.append(null, 0, null);
+    }
+}