Test that we correctly back up an empty file.

(It turns out that we do.  It didn't used to work, I'm not
sure what changed)

tests/backup/src/com/android/backuptest/BackupTestAgent.java

@@ -23,7 +23,8 @@ public class BackupTestAgent extends BackupHelperAgent
 {
     public void onCreate() {
         addHelper("data_files", new FileBackupHelper(this, BackupTestActivity.FILE_NAME));
-        addHelper("more_data_files", new FileBackupHelper(this, "another_file.txt", "3.txt"));
+        addHelper("more_data_files", new FileBackupHelper(this, "another_file.txt", "3.txt",
+                    "empty.txt"));
     }
 }
 

tests/backup/test_backup.sh

@@ -12,6 +12,7 @@ adb shell "rm /data/data/com.android.backuptest/files/* ; \
            echo -n first file > /data/data/com.android.backuptest/files/file.txt ; \
            echo -n asdf > /data/data/com.android.backuptest/files/another_file.txt ; \
            echo -n 3 > /data/data/com.android.backuptest/files/3.txt ; \
+           echo -n "" > /data/data/com.android.backuptest/files/empty.txt ; \
 "
 
 # say that the data has changed

tests/backup/test_restore.sh

@@ -35,6 +35,7 @@ echo
 check_file file.txt "first file"
 check_file another_file.txt "asdf"
 check_file 3.txt "3"
+check_file empty.txt ""
 
 echo
 echo