fix the core optimize problem

src/test/java/org/embulk/input/filename/TestFilenameInputPlugin.java

@@ -67,6 +67,7 @@ public class TestFilenameInputPlugin
     public void testOrderByModifiedTime() throws Exception{
     
         ConfigSource execConfig  = embulk.newConfig()
+              .set("min_output_tasks","1")
               .set("max_threads","1");
     
         Path path_src =  Paths.get("src/test/resources/testModifiedOrder");
@@ -131,6 +132,7 @@ public class TestFilenameInputPlugin
     public void testTagList() throws Exception{
 
         ConfigSource execConfig  = embulk.newConfig()
+              .set("min_output_tasks","1")
               .set("max_threads","1");
     
         Path path_src =  Paths.get("src/test/resources/testDirList");
@@ -212,8 +214,8 @@ public class TestFilenameInputPlugin
         
         
         dir1.addAll(dir2);
-        //System.out.println(lines);
-        //System.out.println(dir1);
+        System.out.println(lines);
+        System.out.println(dir1);
         assertEquals(lines,dir1);
 
     }
@@ -223,6 +225,7 @@ public class TestFilenameInputPlugin
     public void testDirList() throws Exception{
 
         ConfigSource execConfig  = embulk.newConfig()
+              .set("min_output_tasks","1")
               .set("max_threads","1");
     
         Path path_src =  Paths.get("src/test/resources/testDirList");
@@ -288,8 +291,8 @@ public class TestFilenameInputPlugin
         
         
         dir1.addAll(dir2);
-        //System.out.println(lines);
-        //System.out.println(dir1);
+        System.out.println(lines);
+        System.out.println(dir1);
         assertEquals(lines,dir1);
     }
     
@@ -298,6 +301,7 @@ public class TestFilenameInputPlugin
     public void testContent() throws Exception{
 
         ConfigSource execConfig  = embulk.newConfig()
+              .set("min_output_tasks","1")
               .set("max_threads","1");
     
         Path path_src =  Paths.get("src/test/resources/data");