[rspec-users] Comparing files

George Dinwiddie lists at iDIAcomputing.com
Fri Dec 10 11:30:40 EST 2010


On 12/10/10 9:56 AM, Matt Wynne wrote:
> Hello folks,
> I'm writing some tests for file upload code. The files are binary,
> images mostly. I'm futzing around a bit, trying to figure out how to
> assert that the uploaded file is the same as some golden master. If I
> do this:
> File.read(uploaded_file_path).should ==
> File.read(path_to_expected_file)
> Then when it fails, I get an ugly diff of the difference between the
> binary files. So I'm about to invent something of my own. Has anyone
> got a good pattern for doing this already?

I don't already have it, but I've long wanted to implement a visual 
image diff based on an exclusive-or of the two images.  This would give 
a quick visual demonstration of the differences.

I once saw (but now cannot find) and image compare library that did a 
"fuzzy compare" that wasn't fooled by pixel differences.  I've looked 
for this several times, but haven't been able to turn it up again.  It's 
out there, though, in the scientific community (IIRC) rather than the 
software testing community.

  - George

  Dec. 14 - Agile Richmond in Glen Allen, VA
   * George Dinwiddie *                      http://blog.gdinwiddie.com
   Software Development                    http://www.idiacomputing.com
   Consultant and Coach                    http://www.agilemaryland.org

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