e2fsck external journal
../e2fsck/e2fsck: Filesystem has unsupported feature(s) while trying to open test.img

The superblock could not be read or does not describe a valid ext2/ext3/ext4
filesystem.  If the device is valid and it really contains an ext2/ext3/ext4
filesystem (and not swap or ufs or something else), then the superblock
is corrupt, and you might try running e2fsck with an alternate superblock:
    e2fsck -b 8193 <device>
 or
    e2fsck -b 32768 <device>

Exit status is 8
dumpe2fs external journal
Filesystem volume name:   <none>
Last mounted on:          <not available>
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      journal_dev metadata_csum
Default mount options:    user_xattr acl block_validity
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              0
Block count:              2048
Reserved block count:     0
Free blocks:              0
Free inodes:              0
First block:              1
Block size:               1024
Fragment size:            1024
Blocks per group:         8192
Fragments per group:      8192
Inodes per group:         0
Inode blocks per group:   0
Mount count:              0
Check interval:           0 (<none>)
Reserved blocks uid:      0
Reserved blocks gid:      0
First inode:              11
Inode size:	          256
Required extra isize:     28
Desired extra isize:      28
Default directory hash:   half_md4
Checksum type:            crc32c
Journal features:         journal_64bit journal_checksum_v3
Journal size:             2048k
Journal length:           2048
Journal first block:      3
Journal sequence:         0x00000003
Journal start:            0
Journal checksum type:    crc32c
Journal checksum:         0x661e816f
Journal users:            117f752e-f27d-4f6f-a652-072586a29b82