Changed exception on one test, added another and added comments.

One commented test is performance related and may point to
the original ticket being re-assessed or the test condition
being changed. Other comments relate to tickets which have been raised.
Create an image that can be imported successfully.

The original 1x1 png was failing - issue passed on to Melissa - an 8x8 png
fixes this test for the purpose for which it was intended. It may be better
to move to mock images.
Fix some tests and added a new one.

One test was deleting all scripts as a side-effect. This test has been
disabled and a ne test created with an accompanying ticket.