[SPARK-29999][SS][FOLLOWUP] Fix test to check the actual metadata log directory

### What changes were proposed in this pull request?

This patch fixes the missed spot - the test initializes FileStreamSinkLog with its "output" directory instead of "metadata" directory, hence the verification against sink log was no-op.

### Why are the changes needed?

Without the fix, the verification against sink log was no-op.

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

Checked with debugger in test, and verified `allFiles()` returns non-zero entries. (It returned zero entry, as there's no metadata.)

Closes #28930 from HeartSaVioR/SPARK-29999-FOLLOWUP-fix-test.

Authored-by: Jungtaek Lim (HeartSaVioR) <[email protected]>
Signed-off-by: Wenchen Fan <[email protected]>
(cherry picked from commit 5472170)
Signed-off-by: Wenchen Fan <[email protected]>

Author: HeartSaVioR

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSink.scala

@@ -45,8 +45,7 @@ object FileStreamSink extends Logging {
         val hdfsPath = new Path(singlePath)
         val fs = hdfsPath.getFileSystem(hadoopConf)
         if (fs.isDirectory(hdfsPath)) {
-          val metadataPath = new Path(hdfsPath, metadataDir)
-          checkEscapedMetadataPath(fs, metadataPath, sqlConf)
+          val metadataPath = getMetadataLogPath(fs, hdfsPath, sqlConf)
           fs.exists(metadataPath)
         } else {
           false
@@ -55,6 +54,12 @@ object FileStreamSink extends Logging {
     }
   }
 
+  def getMetadataLogPath(fs: FileSystem, path: Path, sqlConf: SQLConf): Path = {
+    val metadataDir = new Path(path, FileStreamSink.metadataDir)
+    FileStreamSink.checkEscapedMetadataPath(fs, metadataDir, sqlConf)
+    metadataDir
+  }
+
   def checkEscapedMetadataPath(fs: FileSystem, metadataPath: Path, sqlConf: SQLConf): Unit = {
     if (sqlConf.getConf(SQLConf.STREAMING_CHECKPOINT_ESCAPED_PATH_CHECK_ENABLED)
         && StreamExecution.containsSpecialCharsInPath(metadataPath)) {
@@ -125,14 +130,12 @@ class FileStreamSink(
     partitionColumnNames: Seq[String],
     options: Map[String, String]) extends Sink with Logging {
 
+  import FileStreamSink._
+
   private val hadoopConf = sparkSession.sessionState.newHadoopConf()
   private val basePath = new Path(path)
-  private val logPath = {
-    val metadataDir = new Path(basePath, FileStreamSink.metadataDir)
-    val fs = metadataDir.getFileSystem(hadoopConf)
-    FileStreamSink.checkEscapedMetadataPath(fs, metadataDir, sparkSession.sessionState.conf)
-    metadataDir
-  }
+  private val logPath = getMetadataLogPath(basePath.getFileSystem(hadoopConf), basePath,
+    sparkSession.sessionState.conf)
   private val fileLog =
     new FileStreamSinkLog(FileStreamSinkLog.VERSION, sparkSession, logPath.toString)
 

sql/core/src/test/scala/org/apache/spark/sql/streaming/FileStreamSinkSuite.scala

@@ -555,10 +555,12 @@ abstract class FileStreamSinkSuite extends StreamTest {
             }
           }
 
-          val fs = new Path(outputDir.getCanonicalPath).getFileSystem(
-            spark.sessionState.newHadoopConf())
-          val sinkLog = new FileStreamSinkLog(FileStreamSinkLog.VERSION, spark,
-            outputDir.getCanonicalPath)
+          val outputDirPath = new Path(outputDir.getCanonicalPath)
+          val hadoopConf = spark.sessionState.newHadoopConf()
+          val fs = outputDirPath.getFileSystem(hadoopConf)
+          val logPath = FileStreamSink.getMetadataLogPath(fs, outputDirPath, conf)
+
+          val sinkLog = new FileStreamSinkLog(FileStreamSinkLog.VERSION, spark, logPath.toString)
 
           val allFiles = sinkLog.allFiles()
           // only files from non-empty partition should be logged