This might help a tiny bit in eliminating multiple downloads to the same URL in cases where the same request to the server is made in quick succession.
The tests try to emulate this and it currently already works most of the time but maybe we can improve.
The download atom can be checked before the temporary file is created by (spit (str cache-directory new-filename) "")
Currently, resources/random only contains 600x600px images but it would be nicer to bump them to 800px because the convert resizes everything to 800px so the images are kept uniformly.