<MockS3
a-bucket
  a-key                => [21 bytes] '<?xml?><a complic...
  binary               => [19 bytes] b'\xf0\x00\xf0\x...
  empty                => [0 bytes] 
  png                  => [19 bytes] b'\x89PNG\r\n\x1...
  short                => [7 bytes] 'short'
  short-binary         => [16 bytes] b's\x00\xf0hort'
b-bucket
  very-long-key-that-is-way-too-long => [19 bytes] 'but short content'
>
