image_comparison tests


It was drawn to my attention that the baseline_images with the expected
images can gobble up a lot of repository space, so it is best to squash
commits to avoid submitting multiple changes to the baseline_images.

Looking at all the tests that use image_comparison, almost all of them go
with the default value of "tol = 0", in other words anything but an exact
match generates an error.

If we only cared about spotting changes then for these tests we could just
store some sort of checksum on the image data and use that to spot when the
image has changed. Updating a checkum only adds a few bytes to the

The down side of this approach (and it is a big downside) is that when an
image changes you would no longer have the expected image and the diff
available to look at.

The only solution I can think to that is to store the expected images
somewhere else, with the ability to retrieve an image given the checksum,
thus keeping them out of the main repository.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>