QA output created by 189
== create base ==
Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=16777216

== writing whole image ==
wrote 16777216/16777216 bytes at offset 0
16 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)

== verify pattern ==
read 16777216/16777216 bytes at offset 0
16 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
== create overlay ==
Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=16777216 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT

== writing part of a cluster ==
wrote 1024/1024 bytes at offset 0
1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)

== verify pattern ==
read 1024/1024 bytes at offset 0
1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)

== verify pattern ==
read 64512/64512 bytes at offset 1024
63 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
*** done